While it wasn’t exactly the debut that Joe Mack was hoping for, the Miami Marlins’ No. 4 prospect is officially a big leaguer.
Slotting into the No. 7 spot in the lineup and catching a strong outing from Janson Junk, Mack went 0-for-3 with a strikeout in a 1-0 loss to the Philadelphia Phillies. The game was the first of the 23-year-old’s MLB career after the Marlins opted to call him up while demoting Agustín Ramírez to Triple-A Jacksonville.
Mack stands as a key component of Miami’s future, and now a part of their present. As baseball’s 54th-ranked prospect, there has been considerable buzz surrounding the Williamsville, NY native after hitting 21 home runs and sporting a .813 OPS across two minor league stops in 2025 and then producing a standout spring with the Marlins.
And Mack may not be the only new face to make their way to Miami this season. The club’s ever-evolving roster could be in line for further injections of youth, with other MLB-ready prospects inching closer to their own debuts.
Now that Mack is officially in the Marlins’ fold, who might be next to arrive? Technically, the answer will likely be journeyman reliever William Kempner, who was recently recalled to replace a designated for assignment Chris Paddack.
But while the promotion of the Kempner is an undeniably cool moment for a player who has bounced around the minors for the past half decade, here are some call-ups with long-term impact potential who could be on the horizon:
Thomas White, LHP
It might not be long before Miami’s top prospect makes his much-anticipated arrival.
Thomas White had an outside shot of making the team out of training camp, but a Grade 1 right oblique strain quickly shelved those hopes. Now, the 21-year-old is healthy and back dominating hitters. After a brief rehab stint at Single-A Jupiter, he has returned to Jacksonville without missing a beat, sporting a 2.13 ERA across three starts and 12.2 innings while striking out 19.
The Marlins will be patient with White, given his age, injury history and the fact that he’s never pitched 100 innings in a season. That patience, though wise for his long-term development, could be an obstacle in any imminent path to the majors. But if the club eventually pulls the trigger on a much-rumored Sandy Alcantara trade, don’t be surprised to see the lefty arrive as a late season call-up.
Robby Snelling, LHP
If White is working his way towards a major league call-up, fellow southpaw Robby Snelling might be already knocking on the door. Through six starts in Jacksonville thus far, he owns a 3-1 record with a 1.86 ERA while amassing 44 strikeouts over 29 innings pitched.
Snelling’s opportunity could come sooner rather than later. Just as Mack benefited from the early season struggles of Ramírez to make the jump, he appears poised to earn a starting spot in the aftermath of Paddack (0-5, 7.63 ERA) being DFA’ed on Tuesday.
Kemp Alderman
Miami currently ranks 21st league-wide in runs per game (4.17), and a lack of production from the outfield stands as one of the key reasons behind those offensive struggles. Jakob Marsee and Owen Caissie, in particular, have endured some growing pains at the plate.
Perhaps Kemp Alderman could help provide a boost? Drafted in the second round of the 2023 MLB Draft out of the University of Mississippi, the versatile outfielder is a little over a year younger than Marsee and only a month younger than Caissie. Most importantly, his offensive numbers at Jacksonville this season (.302/.388/.491 with five home runs) highlight a player that could give the Marlins a much-need spark with the bat.
Miami continues to retool on the fly, weaponizing a strong farm system by continuing to get younger while looking to remain competitive in the NL East. Now with Mack in the fold and Kempner set to arrive, it seems like we could be seeing the arrival of other freshly-minted big leaguers to come.
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