This week, the Boston Red Sox selected top pitching prospect Payton Tolle’s contract and added him to the 40-man roster – a move that prevents him from being eligible for the Rule 5 Draft this winter. While that was undoubtedly the right move for Boston, Tolle's roster spot came at the expense of leaving someone else exposed.
Any prospects who were signed at 18 or younger and have not been added to their club's 40-man roster within five seasons of their signing are at risk of getting snatched up by another team in the December Rule 5 Draft, which allows clubs without a full 40-man roster to select certain non-40-man roster players from other clubs. The Red Sox have a handful of players who fit the bill and may now find themselves on the chopping block as a result of Tolle's addition to the roster.
Fortunately, top prospects like Jhostynxon Garcia and Hunter Dobbins had already been added to the Red Sox's 40-man roster this year before they could become Rule 5-eligible. However, there are still some other names to keep an eye on in Boston's farm system.
Now that the Red Sox have added Payton Tolle to their roster, these prospects are in danger of being exposed in the Rule 5 Draft
Allan Castro, OF (Double-A Portland)
A switch-hitter with average bat speed and above-average raw power, outfield prospect Allan Castro is exactly the kind of bat a rebuilding club could stash if the Red Sox choose not to protect him. Boston's No. 22 prospect according to MLB Pipeline, Castro is currently enjoying the best offensive season of his career at Double-A Portland with 86 hits through 84 games and a .275 batting average.
Castro, whom the Red Sox signed out of the Dominican Republic for $100,000 as a 17-year-old in 2019, has yet to play a game above the Double-A level. However, given his blend of switch-hit feel and athletic corner outfield fit, he could be a real protection candidate if Boston can find away to squeeze him on.
Yordanny Monegro, RHP (Double-A Portland, injured)
Castro's Double-A teammate and fellow countryman, Yordanny Monegro, will also be Rule 5-eligible this winter if the Red Sox don't add him to their 40-man roster. The 22-year-old, who signed with Boston for $35,000 in 2020, saw his 2025 campaign cut short when he underwent Tommy John surgery in June.
Before his injury in Double-A, Monegro missed bats but ran into damage when playing from behind. His career ERA sits at 3.22, and he projects as a multi-inning middle reliever at the big league level.
Rule 5 picks can be stashed on the MLB injured list but must later accrue 90 active days – so injured arms are harder (though not impossible) to carry. Monegro's talent-to-roster-cost calculus probably lowers the immediate risk that he gets poached at the Rule 5 Draft, yet a club could still roll the dice for 2026 value.
The bottom line? Castro – a healthy, rising, Rule 5-eligible prospect – feels like the most likely protection squeeze if Boston needs 40-man roster space this winter.
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