Trusting a rookie to fill a key role is always a risky move for a contending team.

That's not to say it can't pay major dividends.

Just last season, first-year players Gleyber Torres, Miguel Andujar, Walker Buehler and Ronald Acuna Jr. all played key roles in helping their teams reach the postseason.

For rebuilding teams, the decision to leave a clear path to the majors for a top prospect is an easy one.

Vladimir Guerrero Jr. for the Toronto Blue Jays, Fernando Tatis Jr. for the San Diego Padres, Eloy Jimenez for the Chicago White Sox—no offseason additions will be made to block these guys. The doors will swing wide-open once they're deemed MLB-ready.

On the other hand, contending teams run an obvious risk when they put all their eggs in the prospect basket.

With all of that in mind, ahead is a look at six MLB-ready prospects who represent better options to fill areas of need for contenders than any of the available alternatives in free agency or on the trade block.

Keston Hiura, Milwaukee Brewers

The Position of Need: Second base

The Alternatives: Brian Dozier (FA), Josh Harrison (FA), DJ LeMahieu (FA), Jed Lowrie (FA)

At the start of the offseason, the Milwaukee Brewers made the somewhat surprising decision to non-tender Jonathan Schoop, who was acquired at the trade deadline for a package of Jonathan Villar, Jean Carmona and Luis Ortiz.

That leaves a hole to fill at second base.

Brian Dozier (per Ken Rosenthal of The Athletic) and Josh Harrison (via Jon Heyman of Fancred) are two stopgap options the team is rumored to have shown some level of interest in so far this offseason. Cory Spangenberg also signed a one-year, $1.2 million deal after he was cut loose by the San Diego Padres.

No one should stand in the way of Keston Hiura once he's ready.

Arguably the best pure hitter in the minors not named Vladimir Guerrero Jr., Hiura hit .293/.357/.464 with 34 doubles, 13 home runs, 43 RBI and 74 runs scored between High-A and Double-A.

MLB.com wrote: "Hiura has a short, impactful right-handed stroke with a ton of bat speed and outstanding feel for the barrel. He projects to hit for a high average and shows at least average in-game power, with the ball coming off of his bat differently than most to all fields."

A strong start in the upper levels of the minors could have him ready to take over the everyday job before the All-Star break.

With that in mind, Spangenberg should be a suitable short-term solution.

Carter Kieboom, Washington Nationals

The Position of Need: Second base

The Alternatives: Brian Dozier (FA), Marwin Gonzalez (FA), Josh Harrison (FA), DJ LeMahieu (FA), Jed Lowrie (FA)

The Washington Nationals have been linked to several different middle infielders this offseason, but that doesn't mean they're a sure bet to make a signing.

In fact, general manager Mike Rizzo sounds confident with his in-house options, telling Jesse Dougherty of the Washington Post: "We like our situation in the middle of the infield with Trea [Turner] and Howie [Kendrick] and [Wilmer] Difo and [Carter] Kieboom in the wings."

The final name on that list is the one to watch.

Kieboom, 21, has hit well at every stop since he was taken with the No. 28 pick in the 2016 draft.

He posted a .280/.357/.444 line with 31 doubles, 16 home runs and 69 RBI between High-A and Double-A last season, showing strong on-base ability (10.4 BB%) and good contact skills (19.5 K%) to go with his budding power.

A .295 average and .427 on-base percentage over 96 plate appearances in the Arizona Fall League provided further support to the idea that he's close to MLB-ready.

Kendrick and Difo are more than capable of serving as stopgap options until Kieboom forces his way into the picture. At the very least, Washington shouldn't be considering a free-agent addition on anything beyond a one-year deal.

Jesus Luzardo, Oakland Athletics

The Position of Need: Starting pitcher

The Alternatives: Clay Buchholz (FA), Marco Estrada (FA), Gio Gonzalez (FA), Edwin Jackson (FA), Ervin Santana (FA)

Connor Byrne of MLBTradeRumors wrote the following while identifying starting pitching at the biggest remaining need for the Oakland Athletics:

"In true A’s fashion, they’re probably not going to make a big-money splash in free agency, but there are enough affordable veterans out there who could emerge as the [Trevor] Cahill, [Brett] Anderson or [Edwin] Jackson of next year’s team."

As it stands, the projected rotation could be described as patchwork at best.

Mike Fiers was brought back on a two-year deal and is on track to earn the Opening Day nod. Following him will be some combination of Daniel Mengden, Chris Bassitt, Frankie Montas, Aaron Brooks, Paul Blackburn and Tanner Anderson.

While that group provides varying levels of upside and there are still some intriguing buy-low options available on the free-agent market, the real answer to bolstering the rotation could be top prospect Jesus Luzardo.

The 21-year-old is squarely in the conversation for the title of best pitching prospect in baseball after he went 10-5 with a 2.88 ERA, 1.09 WHIP and 129 strikeouts in 109.1 innings spanning three minor league levels. After closing out the season in Triple-A, he's knocking on the door.

With a devastating fastball/changeup/slider repertoire and 60-grade command, he could very well be the present and future ace of the Oakland staff.

Sean Murphy, Oakland Athletics

The Position of Need: Catcher

The Alternatives: Francisco Cervelli (Trade), Martin Maldonado (FA), Russell Martin (Trade), Devin Mesoraco (FA), Matt Wieters (FA)

The Oakland Athletics showed some interest in re-signing veteran catcher Jonathan Lucroy, offering him a one-year, $4 million deal that would have represented a $2.5 million pay cut, according to Heyman.

He instead signed with the Los Angeles Angels, and the A's hunt for a starting catcher continues.

Josh Phegley (102 PA, 64 OPS+, 0.3 WAR) and Chris Herrmann (87 PA, 107 OPS+, 0.5 WAR) are currently the only backstops on the 40-man roster, and both are best suited for a backup role.

That said, the front office doesn't necessarily need to go outside the organization to find its answer.

Sean Murphy is one of the best all-around catching prospects in baseball, and after a strong showing at Double-A and a brief taste of Triple-A, he's on the cusp. The 24-year-old hit .288/.358/.498 with 26 doubles, eight home runs and 43 RBI in 289 plate appearances at Double-A Midland.

His offensive production has actually been a pleasant surprise, as his defensive tools are what made him a third-round pick in 2016. As MLB.com wrote:

"Murphy draws raves from evaluators for his athleticism, agility and defensive tools behind the plate. He stymies the running game with plus-plus arm strength and above-average pop times, so much so that only 46 baserunners attempted to steal against him over 91 games in 2017. His blocking, game-calling and receiving skills have all improved in the professional ranks, and club officials consistently praise his ability to handle pitchers."

A broken hamate bone cost him some time in 2018, though he did return to play eight games before the MiLB season was over. As long as there are no lingering effects, he deserves a long look for the starting role this spring.

Austin Riley, Atlanta Braves

The Position of Need: Corner outfield

The Alternatives: Nick Castellanos (Trade), Carlos Gonzalez (FA), Mitch Haniger (Trade), Adam Jones (FA), Nick Markakis (FA), Nomar Mazara (Trade)

The Atlanta Braves' decision to sign Josh Donaldson to a one-year deal has provided a $23 million wall in the path of top prospect Austin Riley at third base.

That doesn't mean he won't see the majors in 2019.

After hitting .294/.360/.522 with 30 doubles, 19 home runs and 70 RBI in the upper levels of the minors, the 21-year-old slugger is ready to make an impact in the majors.

"He looks like he'll fit the power-hitting, run-producing profile in the mold of a Troy Glaus type of player," wrote MLB.com.

According to David O'Brien of The Athletic, the Braves might give Riley a look in the outfield during spring training. He's still viewed as the long-term answer at the hot corner, but slotting him at a corner outfield spot in 2019 could be a way to get his bat into the lineup.

As it stands, the leading in-house candidate to fill the vacant corner outfield spot is Adam Duvall. However, he hit a brutal .132/.193/.151 with one extra-base hit in 57 plate appearances after coming over from the Reds at the trade deadline, so counting on anything from him would be a major risk.

Bringing back Nick Markakis on a one-year deal is a possibility, and given the health woes of Donaldson the past two seasons, there's always a chance Riley sees significant time at third base after all.

One way or another, the Braves need to give one of the game's most promising offensive prospects a chance to make his mark in 2019.

Forrest Whitley, Houston Astros

The Position of Need: Starting pitcher

The Alternatives: Gio Gonzalez (FA), Zack Greinke (Trade), Dallas Keuchel (FA), Seth Lugo (Trade), Robbie Ray (Trade)

The Houston Astros are currently down three starters from last season. Lance McCullers Jr. will spend 2019 recovering from Tommy John surgery, Charlie Morton signed with the Tampa Bay Rays in free agency, and Dallas Keuchel appears destined to take his talents elsewhere as well.

Right-hander Collin McHugh thrived last season in a bullpen role after working exclusively as a starter from 2014-17, and according to Jake Kaplan of The Athletic, he'll return to the rotation in 2019.

That leaves two open spots.

Prospects Josh James and Framber Valdez both showed intriguing potential down the stretch in 2018, while reliever Brad Peacock has 68 career starts—including 21 during the 2017 season. There's also still the possibility of an outside addition, whether it's a trade for someone like Zack Greinke or more of a depth move to sign someone like Gio Gonzalez.

Regardless, blocking Forrest Whitley in any way would be a mistake.

The 21-year-old saw his development slowed a bit last by a 50-game suspension for a violation of the MiLB drug program, but he picked up right where he left off upon returning. In 26.1 inning at Double-A, he posted a 3.76 ERA and 0.99 WHIP with 34 strikeouts while holding opponents to a .160 batting average.

With a towering 6'7" frame, an electric four-pitch mix and plus command, Whitley has frontline potential with little left to prove in the minors.

He could give the team a third ace alongside Justin Verlander and Gerrit Cole by midseason.

All stats courtesy of Baseball Reference and FanGraphs, unless otherwise noted.