We're at a stage in spring training where it's still difficult to say whether a prospect will make the opening day roster, and since the focus of this piece is stashables, not usables, it's kind of an important distinction.
Certainly for prospects like Ian Anderson, Ke'Bryan Hayes and Nick Madrigal, we know the score already. They're in and were never in jeopardy of being out. Andrew Vaughn and Cristian Pache are heavy favorites, and while it's not as clear for Alex Kirilloff, Tarik Skubal and A.J. Puk, all signs are pointing to yes. For others like Nate Pearson (groin) and Spencer Howard (back), it's largely a matter of health.
So just to make the criteria a little easier, I'm limiting my choices for this top 10 to those prospects who haven't appeared in the majors yet. About the only one being excluded, then, is Casey Mize, starting pitcher for the Tigers. OK, so also Jo Adell and Daulton Varsho, but they're technically not prospects anymore, having exhausted rookie eligibility. Let's say all three would slot between four and six on this list.
Having cleared that up, you should consider stashing these prospects on your bench in the hope of a big payoff later. For the top three, I'd say it's a must in all formats. We don't know exactly when they'll be ready to contribute, but it could be soon. And it could be huge.
1) Jarred Kelenic, OF, Mariners
2019 minors: .291 BA (443 AB), 23 HR, 20 SB, .904 OPS, 50 BB, 111 K
Kelenic was getting all the buzz early in camp, both because of how he looked on the field and because he had leverage in the usual service-time dispute following some boneheaded comments by the team's since-ousted president. A groin injury stopped that train in its tracks, but seeing as he's about ready to return to game action, it's still probably just a matter of weeks before we see the 21-year-old in the majors. Everything comes so easily to him, with the potential to contribute across five categories, that you should expect impact production right away. HIs arrival might be partly contingent on fellow prospect Taylor Trammell's performance, though.
2) Wander Franco, SS, Rays
2019 minors: .327 BA (425 AB), 9 HR, 27 2B, 18 SB, .885 OPS, 56 BB, 35 K
Naturally, the top prospect in all of baseball is on this list, but we shouldn't lose sight of the fact he's only 20 and has yet to play a game above A-ball. Still, the Rays pretty much tipped their hand by having him travel with them to the World Series last year, ready to be activated at a moment's notice. Though their shortstop spot is currently filled by Willy Adames, the ever-versatile Rays will be able to find a spot for Franco, with third base representing the easiest path, and his contact skills are so good that I expect an easy transition. It's just a question of whether it's in late April or late June.
3) MacKenzie Gore, SP, Padres
2019 minors: 9-2, 1.69 ERA, 0.83 WHIP, 101 IP, 28 BB, 135 K
It's actually still possible Gore wins a job at the start of the season given the way the Padres are slow-playing Dinelson Lamet's elbow, but other options like Adrian Morejon and Ryan Weathers have already appeared in the big leagues. Plus, some of the control issues that plagued Gore at the alternate training site have shown up in spring training as well. He's close and presents the sort of varied, well-developed arsenal that should thrive in the majors, but in addition to service-time considerations, a little fine tuning may be warranted for the top pitching prospect in baseball.
4) Logan Gilbert, SP, Mariners
2019 minors: 10-5, 2.13 ERA, 0.95 WHIP, 135 IP, 33 BB, 165 K
Gilbert has officially made only one appearance this spring, but it was impressive. He struck out four, including Mike Trout, in two innings. The Mariners believe he's close, featuring two plus breaking pitches and a changeup that was greatly improved at the alternate training site. He commands the strike zone and has already proven effective at Double-A. His biggest issue is that the Mariners aren't expected to contend, which means they can probably hold out until midseason, barring a rash of injuries.
5) Matt Manning, SP, Tigers
2019 minors: 11-5, 2.56 ERA, 0.98 WHIP, 133 2/3 IP, 38 BB, 148 K
A forearm strain left Manning out of the Tigers' pitcher promotapalooza last year, and the offseason additions of Jose Urena and Julio Teheran are making it difficult for them to find room even for last year's call-ups, Tarik Skubal and Casey Mize. Manning has been effective this spring, though, and at 23, after a steady climb up the minor-league ladder, his time has about come. The non-contending Tigers have no incentive to rush him, but they showed with those two call-ups last year that they won't hesitate when the 6-foot-6 horse with the hammer curve makes a loud enough case.
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6) Bobby Witt, SS, Royals
2019 minors: .262 BA (164 AB), 1 HR, 9 SB, .670 OPS, 13 BB, 35 K
It's an aggressive call for a 20-year-old with 37 minor-league games under his belt, but nobody -- well, no other hitter anyway -- has generated the headlines Witt has this spring, from his home runs (which include a massive 484-foot shot) to his maturity at the plate to his awareness in the field. He hasn't been overmatched and certainly doesn't come off like a 20-year-old. It's leading some fans to wonder if he might break camp as the team's second baseman, though that's probably a pipe dream. A midseason promotion seems possible, though, particularly for the team that hurried Brady Singer and Kris Bubic to the majors last year.
7) Jeter Downs, SS, Red Sox
2019 minors: .276 (460 AB), 24 HR, 24 SB, .888 OPS, 60 BB, 107 K
Second base is where Downs ultimately winds up, and my guess is sooner than later. The Red Sox brought in Enrique Hernandez as a placeholder this offseason, but he's better served in the super utility role he filled for the Dodgers. Downs has made an impact every time he's played this spring, earning high marks particularly for his plate discipline and "swing decisions," as manager Alex Cora put it. The Red Sox might hold out until the summer for Super 2 reasons if they're out of contention, but at Triple-A, Downs will potentially be just a hot streak away from getting the call.
2019 minors: .316 BA (174 AB), 2 HR, 14 2B, .831 OPS, 18 BB, 32 K
The Rangers made a point to leave third base open this offseason, and you have to think Jung, their first-round pick in 2019, is the reason. The 23-year-old earned high marks for his approach straight out of the draft and then grew into power, as the Rangers hoped, at the alternate training site last year. He hasn't gotten much of a look this spring, so opening day was never in the offing. But seeing as the team's stated plan for third base is an assortment of retreads like Rougned Odor and castoffs like Charlie Culberson, a changing of the guard is inevitable.
9) Nolan Jones, 3B, Indians
2019 minors: .272 BA (430 AB), 15 HR, 22 2B, .851 OPS, 96 BB, 148 K
Barring something unfortunate happening to Jose Ramirez, the Indians obviously don't have an opening at third base for Jones, but it's telling that the 22-year-old is expected to learn the outfield down at Triple-A. Cleveland's lack of quality options out there borders on notorious, so if Jones picks up the position quickly enough, his bat should give him an easy path to playing time. He's an on-base machine who offers enough power to get the most out of it, but his struggles against left-handers might confine him to platoon duty at the start, making him sort of Jesse Winker-like.
10) Alek Manoah, SP, Blue Jays
2019 minors: 0-1, 2.65 ERA, 1.06 WHIP, 17 IP, 5 BB, 27 K
I mentioned no other hitter has gotten the headlines Witt has this spring, but one pitcher has. Manoah has blown away the Yankees twice, striking out 11 while allowing just one baserunner in five innings. And it wasn't a bunch of minor-leaguers wearing Yankee uniforms either. We're talking actual regulars. Problem is the 23-year-old has so far played at only short-season Class A, throwing 17 innings. It's a bigger issue for a pitcher than a hitter because of concerns like workload and buildup. Still, given his age, it's not unthinkable Manoah contributes in some capacity if he dominates the minors as thoroughly as he has the Grapefruit League.