DETROIT -- The Tigers spent much of the offseason so far clearing out space on their 40-man roster. Monday was the day for them to stock it up again, adding prospects to protect from the Rule 5 Draft ahead of an 8 p.m. ET deadline.
The club purchased the contracts of catcher Grayson Greiner, shortstop Sergio Alcantara, outfielder Mike Gerber, left-hander Gregory Soto and right-handers Gerson Moreno, Spencer Turnbull and Eduardo Jimenez. The Tigers also signed free-agent left-hander Ryan Carpenter to a one-year Major League deal.
The moves leave the Tigers' roster at 39. Teams must have at least one spot open to participate in next month's Rule 5 Draft, where the club is expected to be active. Teams can and will add and subtract players in the meantime as free agents sign and clubs make trades.
Gerber is the Tigers' highest-ranked prospect to be added -- he's 10th on MLBPipeline.com's list. His left-handed bat and defensive versatility provides in-house depth now and a potential long-term fix later. The 25-year-old has played in just four games above Double-A Erie, finishing the season in Toledo following September callups. But with a .291 career batting average and an .835 OPS in the Minors, he's on a track to reach the Majors at some point next season.

Soto (No. 12) would've been a reach for another club to try to keep on a Major League roster after just five appearances above Low Class A ball, but his breakout 2017 season and lefty arm could have interested in a team in full rebuilding mode. The 22-year-old Soto, who went 12-2 with a 2.25 ERA, allowed just 97 hits over 124 innings with 144 strikeouts.

The Tigers acquired Alcantara (No. 24) in July from the D-backs as part of the J.D. Martinez trade. Some believe the slick-fielding 21-year-old could field his position in the big leagues right now despite not playing above Class A Advanced Lakeland. How much he'll hit is the question, both now and long term.
Moreno (No. 25) is the latest hard-throwing reliever to climb the Tigers' developmental ladder. He dominated Florida State League pitching at Lakeland before advancing to Erie, combining for 66 strikeouts over 50 1/3 innings between the two stops. Moreno has continued the trend with a strong Arizona Fall League campaign. He's the latest potential late-innings reliever coming up through the Tigers' system, and the type of arm teams like to stash in their bullpen for a year.
Turnbull (No. 28) is a former second-round pick out of Alabama. The hard-throwing righty has battled injuries, but he went 7-3 with a 3.05 ERA in 15 starts at Lakeland to earn a late-season stint in Erie. He then went back to the Arizona Fall League and strung together solid outings following a rough debut, finishing 2-2 with a 3.74 ERA to go with 19 strikeouts over 21 2/3 innings. The Tigers still see Turnbull as a starter, but some believe he has the arsenal and arm strength to convert to relief.

The Tigers have some catching depth in their system with Jake Rogers coming over from the Astros in the Justin Verlander trade, but they like the potential of the 6-foot-6 Greiner, whose defensive skills behind the plate belie his body frame. He could be in position to serve as catching insurance if James McCann or John Hicks spend time on the disabled list next season, though the Tigers might still add a veteran catcher as insurance in the John Holaday mold.
Jimenez wasn't ranked among Tigers' Top 30 prospects, but the 22-year-old posted impressive numbers in 34 games between West Michigan and Lakeland. In addition to 12 saves, he posted a 2.13 ERA while striking out 60 batters over 50 2/3 innings. One reason for his limited time was a 30-day suspension he served for throwing a ball into an opponent during an on-field scuffle at West Michigan in May.
Carpenter spent the past four seasons in the Rockies' system, the last two years at Triple-A Albuquerque. The 27-year-old went 10-9 with a 4.15 ERA in 27 outings, 25 of them starts, while striking out 161 batters over 156 innings this season.
Among the Tigers' prospects left unprotected are relievers Adam Ravenelle and Paul Voelker. Ravenelle spent Spring Training in big league camp and was viewed as a relief prospect to watch, but a spring injury and a 5.16 ERA over 42 appearances at Double-A Erie left him behind while younger relief prospects like Zac Reininger and Bryan Garcia passed him.
Voelker, a hard-throwing right-hander, missed 50 games due to suspension, but he struck out 40 over 36 innings with a 2.00 ERA across three levels, ending at Triple-A Toledo. He could be a strong candidate for another club to grab in the Rule 5 Draft.

Also left open to draft is infielder Kody Eaves, who hit .337 (28-for-83) with five doubles, two triples, three home runs and nine RBIs in the Arizona Fall League. He hit .271 with 13 homers and 42 RBIs in 96 games between Erie and Toledo.