While the San Francisco 49ers still boast a decently talented roster after this past offseason, there’s no doubt they’ve seen a substantial talent drain. Patrick Willis, Justin Smith and Chris Borland have retired.  Mike Iupati, Chris Culliver, Perrish Cox, Michael Crabtree, Frank Gore and Stevie Johnson have left in free agency. While the 49ers have intriguing options and backup plans at each and every one of those positions, it’s still a big bundle of uncertainty and potential.

This is why ESPN dropped the 49ers to 22nd in their future power rankings. As Mike Sando put it, “it is unlikely all the changes will work out in the negative so resoundingly, but at best, the unknowns cloud the future.”

So, let’s replace the unknowns with some knowns. One way I like to preview the upcoming season is to take a look at the teams the 49ers are playing and decide who they would grab from their opponent’s rosters. It’s a way of evaluating the strengths of opponents and the weaknesses of the 49ers in a different perspective.

We did this exercise last season with a 49ers team that was, on paper, much more talented—or, at least, less filled with question marks. The dramatic shift in the 49ers’ roster composition, however, might make a dramatic shift in which players are actually taken.

We’re not considering salary cap implications or future potential here—we’re strictly getting the best players for the 2015 season. In this exercise, the 49ers have to take one—and only one—player from each of their 13 2015 opponents to fill one of their 24 starting slots, including a nickel cornerback and slot receiver.

The one-per-team rule means, for example, the 49ers can’t end up with Aaron Rodgers and Jordy Nelson and Randall Cobb and Josh Sitton from the Green Bay Packers. It also means they have to pick someone from everyone, even if the pickings are slim, as they are on, say, the Cleveland Browns.

Here’s my attempt at putting together the best roster possible with those restrictions.

Minnesota Vikings: RB Adrian Peterson

As high as I am on Carlos Hyde—and I’m very excited for his potential going forward—being able to add a former MVP player like Adrian Peterson to replace Frank Gore would be a massive upgrade. The 2012 MVP should still be effective as he turns 30 years old.

Normally, missing essentially an entire season would be a red flag for a player, but in Peterson’s case, it probably actually helps. Peterson didn’t miss the 2014 season due to injury; he missed it thanks to a suspension. That’s one less year of pounding at the most physical position in football, as well as 200-300 less carries on his odometer. The year off might actually refresh him, leading to another great rushing campaign.

With the 49ers not taking on the Eagles or Chiefs this year, the selection of Peterson as the running back comes a bit easier. You can make a strong argument for Marshawn Lynch being the best running back the 49ers face in 2015, but the Seahawks have a more talented roster overall, so there are plenty of other alternatives there. I also briefly considered safety Harrison Smith, but Eric Reid and Antoine Bethea have better track records in the NFL than Carlos Hyde has.

Give me Peterson and his career 5.0 yards per carry, and the 49ers will be successful at running the ball.

Other players considered: C John Sullivan, DE Everson Griffen, S Harrison Smith,

Pittsburgh Steelers: QB Ben Roethlisberger

The 49ers face a very tough run of quarterbacks in 2015. Roethlisberger and Aaron Rodgers are two of the best in football. Russell Wilson and Matt Ryan are two of the most promising young players around. Eli Manning and Joe Flacco boast Super Bowl rings. Matt Stafford has perhaps the biggest arm in the game.  The list goes on.

While I think Colin Kaepernick will bounce back in 2015, I’m not passing up on the opportunity to improve at the position, and that’s why I’m grabbing Roethlisberger. Roethlisberger topped Football Outsiders’ DYAR rankings last season and was third in Pro Football Focus’ rankings. He had the best year of his career at age 32, showing no signs of slowing down.

There’s not a better pure thrower in the sport. We know he can hit the deep ball with regularity; he found Martavis Bryant quite frequently last season. Giving him a top deep threat like Torrey Smith would pay huge dividends. He also can absorb a pass rush, which would have been useful last season with the 49ers’ leaking offensive line.

I was torn between Roethlisberger and a Packers receiver or Aaron Rodgers and Antonio Brown. Both options are entirely justifiable, but in the end, I went with Football Outsiders’ top volume quarterback over their top per-play quarterback. You really can’t make a wrong pick here.

Other players considered: WR Antonio Brown, RB LeVeon Bell, OT Kelvin Beachum

Arizona Cardinals: DE Calais Campbell

The 49ers need to replace both starting defensive ends entering 2015, with both Justin Smith and Ray McDonald gone. Only seven of the 49ers’ 13 opponents run a 3-4 defense, which sort of limits the possibilities here. Fortunately, there is one elite 3-4 end on the 49ers’ schedule, and that’s Calais Campbell.

Campbell was the pick from the Cardinals last season as well, and the 49ers have only gotten worse at the position while Campbell has gotten better. He made his first Pro Bowl last season, though he’s deserved to go in the past. He’s not the best 3-4 end in football and won’t be as long as J.J. Watt is being insane down in Houston, but he’s right in the mix with Sheldon Richardson and Fletcher Cox to be that second guy.

He’s an incredible pass-rusher for an interior lineman, winning one-on-one battles with left tackles and guards. He simply has to be double-teamed in the run game, or he’s going to use his raw size and leverage to move people out of his way and live in the backfield. The 49ers just hope their giant, Arik Armstead, develops into half the player the 6’8”, 300-pound Campbell already is.

Other players considered: OT Jared Veldheer, OG Mike Iupati, CB Patrick Peterson

Green Bay Packers: WR Randall Cobb

The slot receiver position is essentially a starting role in the modern NFL. Teams use three wide-receiver sets with more and more regularity, and receivers who were once considered too small to compete in the NFL are thriving, matched up with nickel corners and safeties.

The single best slot receiver in the game right now is Randall Cobb. He’s a terror in the slot, bringing an elite mix of balance and quickness opposing cornerbacks cannot match. Cobb has great leaping ability, a huge catch radius and a spectacular ability to break down coverages and find the open space. Cobb exploded to career-highs of 91 receptions and 1,287 yards last season, making what is likely to be the first Pro Bowl of many.

The 49ers use Anquan Boldin as their primary slot receiver. While Boldin still produces very well, with solid hands and great third-down abilities, he’s not Cobb. There’s only two slot receivers the 49ers face in 2015 that I’d place above Boldin—Cobb is one, and Andrew Hawkins in Cleveland is the other.

I almost decided to keep Boldin over Cobb, too, because the Packers feature the most loaded roster the 49ers will face in 2015. Aaron Rodgers might be the best quarterback in football. Jordy Nelson would represent a massive upgrade over either Bruce Ellington or Quinton Patton as a receiver. Josh Sitton would be the perfect replacement for Mike Iupati.

Quarterback, outside receiver and guard have plenty of options, however. The 49ers don’t have as many top slots receivers on their schedule, so Cobb becomes the pick.

Other players considered: QB Aaron Rodgers, WR Jordy Nelson, OG Josh Sitton

New York Giants: CB Trumaine McBride

This one requires a little bit of explaining.

McBride isn’t the best player on the Giants. That likely goes to Odell Beckham. He’s also not the best cornerback on the Giants, because that’s Dominique Rodgers-Cromartie, who was the choice last year.  Jason Pierre-Paul and Johnathan Hankins are also better players than McBride is. So why McBride?

To run down the other players real quick: the Giants use a 4-3 front, so neither Pierre-Paul nor Hankins are a perfect fit for the 49ers’ front. Yes, adding 13 players to the team could involve shifting fronts, but when there are other options available, I try to avoid that. So they’re out.

Beckham had an amazing rookie season, but it was just one year—and not even a full year, as he played in only 12 games last season. He’s great and amazing and worth going crazy over, but the 49ers play a lot of good receivers this year. Antonio Brown, Jordy Nelson, Randall Cobb, Julio Jones, A.J. Green, Calvin Johnson—the 49ers have tons of choice there, with longer track records than Beckham has.

That left cornerback, the 49ers' weakest position. I had already added someone on the outside, who we’ll get to in a couple slides, so I was left with a couple choices. I could either move Dominique Rodgers-Cromartie inside to the slot, or decide if the gap between Rodgers-Cromartie and Tramaine Brock or the gap between McBride and Jimmie Ward was larger.

In the last two seasons, Rodgers-Cromartie has spent just 32 snaps in slot coverage, according to Pro Football Focus—it’s just not his position. While he’s talented enough to play there, and did some for Philadelphia, he’s better on the outside matched up against No. 1 receivers.

It was McBride the Giants moved inside when injury issues started to pile up, though a broken thumb eventually removed McBride from the rotation as well. McBride has a better body type to handle shifty slot receivers anyway, and he does better than DRC at limiting yards after the catch.

I also have a lot more confidence in Brock, who had an excellent 2013 season before missing most of last season with injury, so finding a replacement for Ward is a higher priority. Thus, McBride is the pick, though I acknowledge it’s probably the least exciting pick of the bunch. If you took DRC instead and opted to move Brock inside, I couldn’t blame you too much.

Other players considered: WR Odell Beckham, DE Jason Pierre-Paul, CB Dominique Rodgers-Cromartie

Baltimore Ravens: OG Marshal Yanda

Mike Iupati was one of the best run-blocking guards in football. Yes, he was one-dimensional and not particularly successful in the passing game, but he paved ways for running backs like few others. In fact, he was Pro Football Focus’ second-highest rated guard in the run game in 2014. He will be missed.

The one player who graded higher than Iupati? Ravens guard Marshal Yanda. Yanda’s also a better run-blocker than pass-protector, but that’s only because he’s so darn good in the run game. He can succeed in a man-blocking scheme like the 49ers used last year or a zone scheme like they’re moving to in 2015—he’s versatile.

And, as for his “lesser” pass-blocking traits? Well, he only allowed one sack last season, according to Pro Football Focus, and only a total of 16 pressures. That’s “only” good for a tie in 24th, but it’s almost half of what Iupati gave up last season, and still well in the range of top guards. Couple that to his elite run-blocking talent, and you can see why Bleacher Report’s Matt Miller ranked him as the best guard in football last season. He’s certainly a better option than the promising yet unproven Brandon Thomas.

Other players considered: G Kelechi Osemele, LB C.J. Mosley, LB Daryl Smith

Seattle Seahawks: CB Richard Sherman

He’s brash, he’s arrogant, he’s cocky—and he backs it up on the playing field. Is Richard Sherman the best cornerback in football? You can make arguments for a number of players, but Sherman’s in that very short list.

Sherman’s level of respect is legendary, with Aaron Rodgers not targeting him a single time on national television in the Week 1 opener last season. He was only targeted 65 times all season long last year, according to Pro Football Focus. That’s one target every 8.5 snaps he was in coverage, which led the league, as did his 17.8 coverage snaps per reception. His 0.76 yards given up per snap he was in coverage was second to only Chris Harris.

Sherman was the pick last year and will likely be the pick for years to come, though he had more competition from the offense this year with the addition of Jimmy Graham. You can’t go wrong with adding someone like Sherman to your roster, however—as the 49ers learned with Deion Sanders, it’s better for the great cornerback to be trash talking for you rather than against you.

Other players considered: RB Marshawn Lynch, TE Jimmy Graham, S Earl Thomas

St. Louis Rams: DE Robert Quinn

The Rams were the hardest team to find a player by far.

There is no one on offense I’d take over the 49ers’ current starter.

You could make arguments for Kenny Britt or Stedman Bailey as wide receivers over Bruce Ellington or Quinton Patton. You could argue for Jared Cook over Vernon Davis. You could argue for Todd Gurley over Carlos Hyde. You could argue for Roger Saffold over Brandon Thomas. 

All of these, however, are at best debatable—there’s no obvious offensive positions where the Rams are better off than the 49ers. If you were to merge the two franchises, you could make a strong argument for just bringing over the 49ers offense verbatim.

Ah, but the Rams' calling card is their defense, right? They ranked sixth in weighted DVOA last season according to Football Outsiders, one slot behind the 49ers. Considering the 49ers’ losses, it should be easy to find replacements, right?

Well, not so much. The Rams run a 4-3 front, so if we take any of their front seven, they’d be playing slightly out of position. That would just leave us with cornerback, and while E.J. Gaines or Janoris Jenkins are probably better than Shareece Wright, that’s not exactly thrilling, either.

So, making the best out of a poor situation, we’re moving Robert Quinn to 3-4 end and grabbing him, just as we did last season.  Quinn was Bleacher Report's fourth-rated 4-3 end last season, and he’s a massive threat as a pass-rusher, where he’s racked up 29.5 sacks over the last two seasons. 

He probably is more suited for an outside linebacker role in San Francisco’s defense, but the 49ers used a decent number of four-man line concepts last season. I really think a competent defensive coordinator could find some way to plug Quinn into the 49ers defense and let him terrorize quarterbacks, even if the fit isn’t perfect.

Other players considered: DE Chris Long, CB E.J. Gaines, CB Janoris Jenkins

Atlanta Falcons: WR Julio Jones

I knew I was going to take one of the elite wide receivers the 49ers faced this season. The question was simply: Which one? That came down to the quality of the other players on the team more than anything.

Antonio Brown had to deal with Ben Roethlisberger, one of the top quarterbacks in the game.

Jordy Nelson got pipped by Randall Cobb, another elite receiver for a harder-to-find role.

Odell Beckham Jr. only has one season of experience, so I went with a lesser veteran.

A.J. Green might be the best player on the Bengals, but there’s a lineman I wanted after Anthony Davis’ departure.

Calvin Johnson’s slowly entering the downside of his career, and I feel he’s only very, very good now, as opposed to elite.

That leaves Jones, who I feel is the best route-runner in football. He set career highs in receptions and yards last season, and has the ideal body type to be a deep threat or to catch balls over the middle.  With Jones added to Randall Cobb and Torrey Smith, the 49ers have the best receiving corps in the NFL.  Ben Roethlisberger will be spoiled for choice with this set.

Other players considered: QB Matt Ryan, OG Jon Asamoah, CB Desmond Trufant

Chicago Bears: TE Martellus Bennett

Last year, I had the 49ers taking Brandon Marshall from the Bears, grabbing a tall target for the passing game. With Marshall gone to New York, I’ll keep the same logic at a different position, grabbing the 6’6”, 265-pound Bennett to upgrade over Vernon Davis’ disaster of a 2014 season.

With two deep threats in Torrey Smith and Julio Jones, we don’t need our tight end to go deep downfield.  We need someone with solid hands, which Bennett showed with 90 receptions last year, leading all tight ends. He had a catch rate of 72 percent, which isn’t perfect but is more than solid enough for our purposes.

Bennett’s also a solid blocker in the running game, as well—he’s not just a big-bodied receiver. Pro Football Focus has him as their eighth-best run-blocker last season, and several of the players ahead of him were strictly blocking tight ends. 

Bennett had more receptions than any of the tight ends ahead of him on the blocking list, so if you’re looking for an all-around tight end, as opposed to a great receiving tight end like Rob Gronkowski, Bennett might be second only to Travis Kelce.

The 49ers have plenty of players at tight end, but they’re all question marks. Bennett solidifies the position.

Other players considered: WR Alshon Jeffery, LB Pernell McPhee, CB Alan Ball

Cleveland Browns: LB Karlos Dansby

The Browns might be the worst team on the 49ers’ 2015 schedule, but their strengths actually match up pretty nicely with San Francisco’s weaknesses. There are a number of interesting names on their offensive line to build around, and you could make arguments for every single player in their secondary over the equivalent 49er.

However, I’ll choose to take linebacker Karlos Dansby from them to stick alongside NaVorro Bowman in the center of the defense. Dansby was PFF’s ninth-rated inside linebacker last season, and third behind only Luke Kuechly and Jerrell Freeman when it came to pass coverage. This despite missing a month of the season with a sprained MCL.

Dansby probably should have made the Pro Bowl in 2013 with Arizona, and he hasn’t really gotten the credit he deserves as a top linebacker in football. He’s certainly a more proven quality than Michael Wilhoite, and he would nicely fill the void left by Patrick Willis and Chris Borland.

He’s not the best player on the team—that goes to Joe Thomas, their stalwart left tackle. The 49ers already have a top left tackle, though, and Wilhoite might be their weakest starter. Dansby it is.

Other players considered: OT Joe Thomas, OG Joel Bitonio, C Alex Mack

Cincinnati Bengals: OT Andrew Whitworth

The departure of Anthony Davis leaves the 49ers scrambling a little bit, either using Erik Pears, Alex Boone or Trent Brown at right tackle for at least a season. We can do better than that if we can take a player from any team.

Of course, Andrew Whitworth is not a right tackle. He played all 16 games at left tackle last season, and he was a tackle and a guard the year before. He hasn’t played a single snap on the right side of an offensive line since he entered the league in 2006.

However, this isn’t like shifting from a 4-3 end to a 3-4 end. The tackle positions aren’t quite interchangeable, but the duties and responsibilities of a left tackle are much more difficult than a right tackle, thanks to protecting the quarterback’s blind side and being matched up against the top pass-rushers. If you can succeed on the left, you can succeed on the right—it’s not always the case the other way around.

So, whether you plug Whitworth in at right tackle or move him over to the left and have Joe Staley move to the right, you’re talking about a pair of elite bookends for the offensive line.  That would be the best tackle combination in football, bar none. One of them can learn to play the right side.

Other players considered: WR A.J. Green, OG Kevin Zeitler, DL Carlos Dunlap

Detroit Lions: S Glover Quin

While Eric Reid has done very well in his two seasons in the league, he has been prone to concussions. Rumors have had him considering retirement thanks to those concussions, though Niners Nation reports that he has refuted those rumors.

Still, those concerns have to be why the 49ers used a second-round pick on Jaquiski Tartt in the 2015 draft. They could use some insurance in case Reid goes down yet again or decides that the risk of continuing to play is too much.

Rather than reaching for Tartt in the second round, we can grab one of the top free safeties in football in Glover Quin.  Quin was tied for the third-highest safety rating by PFF last season, performing great in coverage and fairly solidly in run support. Only Rahim Moore was used more in coverage than Quin was, and his seven interceptions led the league at the position.  He’s a true coverage safety and would provide a boost even over a healthy Reid at this point.

Other players considered: WR Calvin Johnson, LB Stephen Tulloch, CB Rashean Mathis

Final Roster

Final Roster

After all these moves, here would be the lineup, with current 49ers in bold.

QB: Ben Roethlisberger
RB: Adrian Peterson, Bruce Miller
WR: Julio Jones, Randall Cobb, Torrey Smith
TE: Michael Bennett
OL: Joe Staley, Marshall Yanda, Daniel Kilgore, Alex Boone, Andrew Whitworth

DE: Calais Campbell, Robert Quinn
NT: Ian Williams
OLB: Aldon Smith, Aaron Lynch
ILB: NaVorro Bowman, Karlos Dansby
CB: Richard Sherman, Tramaine Brock, Trumaine McBride
S: Antonie Bethea, Glover Quin

Prefer Rodgers over Roethlisberger? Don’t like the McBride pick for the Giants? Think you can do better? Leave your team in the comments!

Bryan Knowles is a featured columnist for Bleacher Report, covering the San Francisco 49ers.  Follow him @BryKno on twitter.