An uptick in activity on the free-agent market right before NFL training camps get underway isn't unusual as teams look to fill out summer rosters.

But with coronavirus-related opt-outs continuing across the league, there's a heightened sense of urgency to find and sign remaining free agents.

Several teams have unanticipated holes to fill before getting camp workouts started. Players with high snap counts at important positions, even on a rotational basis, make up some of the biggest names to opt out.

Below are the most notable players to do so, and based on production, fit and ability to fill in on short notice, we've included some of the best free agents left who can fill those voids.

DT Josh Tupou, Bengals

Josh Tupou is far from the biggest name on the Cincinnati Bengals defensive line. But he's far from a minimal loss. He played 44 percent of his defense's snaps last year in a key run-stuffing role, earning a 73.8 Pro Football Focus grade.

The defensive tackle projected to fit into the same role in 2020, working as the third tackle behind Geno Atkins and free-agent add D.J. Reader. This was especially important because defensive coordinator Lou Anarumo told Geoff Hobson of the Bengals' official site he wanted a reduced role for Atkins in 2020.

Instead, the Bengals only have unproven names such as Renell Wren to fill Tupou's void after they waived Ryan Glasgow. A free agent such as Domata Peko could help fill the void in run-based packages.

Top free-agent fits: Domata Peko, Mike Daniels, Damon Harrison

G Laurent Duvernay-Tardif, Chiefs

Laurent Duvernay-Tardif of the Kansas City Chiefs was the first NFL player to opt out, and odds are strong he'll remain one of the most important.

Duvernay-Tardif, 29, played in 14 games last year for the Patrick Mahomes-led Chiefs, logging 85 percent of the team's snaps, allowing just two sacks and receiving a PFF grade of 57.2.

Continuity is a big thing for offenses, and his loss could hurt, though the Chiefs at least have some experience with this since Andrew Wylie filled in at this spot in 2018 when Duvernay-Tardif only appeared in five games.

Still, the Chiefs keep finding ways to make big moves underneath the salary cap ($6.3 million remaining), and this might be no exception. While free-agent guard Larry Warford opted out, other veteran options with plenty of experience remain out there. Josh Kline, for example, plays on the right side and is not only strong in the running game but also only let up two sacks over 700-plus snaps in 2019, per PFF.

Top free-agent fits: Josh Kline, Ronald Leary

LT Nate Solder, Giants

New York Giants left tackle Nate Solder will continue to stand as one of the most important players who chose to opt out.

Solder, a big free-agency win for the Giants in 2018, hasn't missed a game since joining the team. And while he wasn't perfect last year, the veteran and 2011 first-round pick was poised to play a key role in not only protecting quarterback Daniel Jones, but also mentoring No. 4 overall pick Andrew Thomas.

Instead, Thomas will be thrown to the wolves on the left side in front of Jones, who suffered 38 sacks last year over just 13 games. That means Cameron Fleming, who received a grade of 59.4 from PFF last year, could start on the right side.

Or the Giants could look to free agency for either a spot starter or depth, especially a seasoned veteran with swing-tackle experience who could come in and at least be a mentor for Thomas, who just lost one of the better mentor figures at his position. Demar Dotson fits the bill as a swing player who can boost depth.

Top free-agent fits: Demar Dotson, Donald Penn, Jared Veldheer

WR Devin Funchess, Packers

The Green Bay Packers brought on free-agent Devin Funchess to presumably give him nice role in three-wideouts sets to assist quarterback Aaron Rodgers.

Instead, the Packers will have to lean heavily on Davante Adams again and hope someone like Allen Lazard can provide a boost.

Funchess, 26, got in just a single game last year with Indianapolis before he broke his collarbone in September.

Before that, he played 14 games in Carolina in 2018, tallying 549 yards and four scores—a performance good enough for a 68.4 PFF grade. While Funchess hasn't always been the most consistent, the fact that he scored 21 times over his first four seasons and has averaged 13.8 yards per career catch projected well in an offense with Rodgers, Adams and a strong backfield.

Options persist, should the Packers want to add another name. A bigger-bodied threat such as the 6'3", 225-pound Demaryius Thomas or a deep threat like Taylor Gabriel would provide some schematic choices.

Top free-agent fits: Demaryius Thomas, Taylor Gabriel, Paul Richardson, Jermaine Kearse

OT Marcus Cannon, Patriots

In the wake of losing quarterback Tom Brady, the New England Patriots at least projected to have a solid offensive front to protect new arrival Cam Newton.

Marcus Cannon's opt-out changed the outlook, though.

He started 15 games in 2019, logging 88 percent of the team's offensive snaps and allowing six sacks on a 68.0 PFF grade. The Patriots could slide franchised guard Joe Thuney over to tackle or entrust the edge to a relative unknown like Yodny Cajuste.

Free agency at least provides a few alternatives who can fill in on the right side in a respectable manner, if not merely provide insurance. There won't be an upgrade available, but passable play plus good schematic planning around Newton's abilities could compensate for the loss.

Top free-agent fits: Demar Dotson, LaAdrian Waddle, Jared Veldheer

DT Eddie Goldman, Bears

Eddie Goldman was one of the more shocking opt-outs.

The Chicago Bears star defensive lineman and No. 39 pick in the 2015 draft had another solid season last year, logging 44 percent of his unit's snaps to the tune of one sack, six pressures and strong play against the run for a 70.7 PFF grade.

It won't be simple to replace the rotational effectiveness that helped the Bears surrender just 18.6 points per game (fourth) and 102.0 rushing yards per game (ninth). There's a steep drop on the depth chart if the team has to turn to Bilal Nichols, and Goldman's opt-out places even more pressure on Akiem Hicks.

Free agency at least offers potential relief, with run-stuffing part-timers still available given the limited importance of the role these days. Even if it's a depth-only add, something is probably better than nothing for a unit that doesn't want to miss a step.

Top free-agent fits: Domata Peko, Mike Daniels, Damon Harrison

LB Dont'a Hightower, Patriots

The hits just keep coming for what will suddenly be a new-look New England Patriots defense in 2020.

After the team lost Kyle Van Noy and Jamie Collins in free agency, linebacker and play-caller Dont'a Hightower opted out of the season.

Hightower, a first-round pick in 2012, has been a key cog since his selection and has logged double-digit games in all but one season since his arrival in Foxboro, Massachusetts. Last year was more of the same, as he got in 15 games and 72 percent of the defensive snaps while posting 71 total tackles, 5.5 sacks and four passes defensed—all good for a 69.4 PFF grade.

The loss means the Patriots are down four of five primary linebackers from a year ago, and it means a bump in role for the likes of John Simon and Brandon Copeland, if not rookies Josh Uche and Anfernee Jennings.

New England could also look to the market in this area, where some experienced players could pick up the defense quickly and play a rotational role to help mitigate the loss. Whether it's a pass-rusher like Clay Matthews or a versatile, every-down upside player like Darron Lee, options exist.

Top free-agent fits: Clay Matthews, Darron Lee, Alec Ogletree, Mychal Kendricks

Salary-cap info via Spotrac.