Since their playoff run ended on Sept. 30, the Boston Red Sox have had their eyes on an impending roster crunch, as seven players who ended the season on the 60-day injured list needed to be returned to the 40-man roster. In total, the Red Sox needed four spots on their 40-man roster to make enough space for the returning players by Monday's 5 p.m. ET deadline.

Chief Baseball Officer Craig Breslow got right to work on Thursday when the offseason officially began, trading outfielder Nate Eaton to the Athletics and infielder Tsung-Che Cheng to the Detroit Tigers. After reportedly spending the day looking for trade partners for the final two roster spots, the deadline has passed, and the team has designated relievers Zack Kelly and Eduardo Rivera for assignment. 

Kelly performed well in his lone stint in Boston in 2026, from April 3 to May 22, posting a 3.31 ERA in 16.1 innings before the team demoted him after calling up fellow right-handed reliever Tyron Guerrero. After being surprisingly optioned, Kelly told MassLive.com’s Chris Cotillo that he would be open to a trade, with Cotillo adding that there had been interest. 

After posting a 6.91 ERA in 10 appearances with Worcester, Kelly landed on the Triple-A injured list with right elbow inflammation. He was later recalled to Boston and placed on the 60-day IL with a stress fracture in his right elbow, where he finished the season. 

After signing with the Red Sox as a minor-league free agent in 2021, Kelly made his major-league debut in 2022. In five seasons serving as an up-and-down reliever, the 31-year-old right-hander posted a 4.04 ERA in 131.1 innings. 

Kelly was out of minor league options heading into the 2027 season, making him a likely candidate to be DFA'd or traded to clear the necessary roster spots. 

After being released by the Athletics in May 2024, Rivera signed with the Red Sox just a month later. After two seasons in the minors, the 23-year-old made his major league debut in April after a surprise promotion following just two Double-A appearances. In total, Rivera made four appearances with the big-league club, posting a 6.30 ERA in 10 innings. The hard-throwing left-hander spent most of the season in Triple-A, posting a 2.96 ERA in 24 appearances and striking out 27.7 percent of the batters he faced. 

Rivera's season came to an early end on Aug. 7 when he landed on the Triple-A injured list with a back strain. Rivera was recalled by the Red Sox on Sept. 1 and placed on the 60-day IL with a lumbar strain, ending his season. 

Triston Casas, Kutter Crawford,  Johan Oviedo, Justin Slaten, and Eli White were all activated off the injured list and placed back on the 40-man roster. 

The Red Sox had reportedly considered adding outfield prospect Allan Castro to the 40-man roster to prevent the 22-year-old from hitting minor league free agency. However, ultimately the team decided against the move, which would have required another spot on the 40-man roster to be cleared. The switch-hitting outfielder spent the 2026 season with Triple-A Worcester, where he hit .252/.325/.397/.722 with 15 home runs, 18 doubles and 20 stolen bases, driving in 77 runs. He'll now head to free agency, where he is free to sign with any team.