BOSTON — The Red Sox have placed third baseman Alex Bregman on the 10-day injured list after an MRI revealed a significant right quad strain.
Top shortstop prospect Marcelo Mayer — who also has played third base and second base in the minor leagues — has been selected to the 40-man roster and will take Bregman’s spot on the 26-man active roster. Mayer will make his major league debut in the second game of Boston’s doubleheader Saturday at 6:35 p.m.
To clear a spot on the 40-man roster for Mayer, Boston placed first baseman Triston Casas on the 60-day IL. Casas ruptured his patellar tendon May 2, then underwent season-ending surgery two days later.
Boston also designated left-handed pitcher Sean Newcomb for assignment and promoted hard-throwing righty Luis Guerrero from Worcester.
Bregman injured his quad running out a single that he hit off the Green Monster on Friday. He underwent an MRI early Saturday.
“Significant injury,” manager Alex Cora said after Boston’s 6-5 10-inning walkoff victory in Game 1. “He’s going to be out for a while.”
Bregman was in the clubhouse after Game 1. He described it as “a pretty severe right quad strain.”
“It is what it is and now try to take it day by day and crush the rehab,” Bregman said.
Both Cora and Bregman said it’s similar to the left quad strain the third baseman suffered in 2021. That injury kept him on the IL from June 17-Aug. 25.
“I’m not going to give you a timetable,” Cora said. “Hopefully, trusting our medical staff, it’s sooner rather than later. But he’s going to be out for a while.”
Bregman was optimistic when he left Fenway Park after Friday’s game. But it began hurting when he tried to fall asleep.
“Last night, couldn’t really fall asleep,” he said.
Bregman was batting .299 with a .385 on-base percentage, .553 slugging percentage, .938 OPS, 11 home runs, 17 doubles, 35 RBIs, 32 runs, 22 walks and 42 strikeouts in 51 games (226 plate appearances).
He agreed the injury is especially tough after how well he began the 2025 season.
“It’s horrible,” he said.
He said there’s no timetable right now.
“It’s just day by day,” he said. “There’s no timetable for it. So just focus on the next step.”
