The Boston Red Sox traded infielder Marcelo Mayer to the San Francisco Giants for left-hander Erik Miller and minor-league outfielder Carlos Gutierrez, the clubs announced Monday.
Mayer was the top-ranked prospect in Boston's system as recently as 2024.
The 23-year-old hasn't played since late June due to a stress reaction in his forearm. He doesn't have a clear timeline to return this season.
Mayer has struggled in the majors, slashing .223/.282/.312 with seven homers and 32 RBIs over 114 games since debuting in 2025.
The Red Sox selected Mayer fourth overall in the 2021 draft.
Miller, meanwhile, has accumulated a 2.76 ERA with 12.4 K/9 across 38 appearances this season. The reliever's under team control through 2029.
The 28-year-old sits in the 99th percentile for average exit velocity against, 97th percentile in whiff rate, and 95th percentile in strikeout rate.
