Giants New Second Baseman Could Begin Injury Rehab Assignment Soon

The San Francisco Giants made several trades at the deadline and most of the return they received was in the form of prospects. There was one notable exception.

Former Boston Red Sox second baseman Marcelo Mayer was part of a trade that sent Giants reliever Erik Miller and center fielder Carlos Gutierrez to Boston for Mayer. It was a fresh start for the former top prospect and there is an open spot for him at second base. That’s because the Giants also traded Luis Arraez at the deadline to the Philadelphia Phillies.

But San Francisco also knew that it would have to wait a bit on Mayer. On June 26 the Red Sox put him on their 10-day injured list with a bone stress reaction to his left ulna. On Friday, the Giants announced that Mayer has made enough progress to be in line for a rehab assignment next week, per NBC Sports Bay Area’s Alex Pavlovic.

Marcelo Mayer’s Next Move

Boston Red Sox short stop Marcelo Mayer swings through a baseball during a game. — Boston Red Sox short stop Marcelo Mayer. | IMAGN IMAGES via Reuters Connect

Mayer is with the team in San Francisco as they host the Detroit Tigers this weekend. The Giants want him to spend a couple of days with the team before he heads to Triple-A Sacramento for his rehab assignment. The River Cats are at home this week against Round Rock. After a day off on Monday, they’ll head to Las Vegas for a week-long series that starts on Tuesday. It’s not clear how long he’ll stay with Sacramento.

Before the injury he was struggling at the plate. He slashed .220/.282/.312 with three home runs and 22 RBI in 70 games. Last year in 44 games he slashed .228/.272/.402 with four home runs and 10 RBI. He missed part of last season with a wrist injury.

Mayer could be the biggest acquisition of the entire trade deadline for San Francisco if he pans out. Boston selected him No. 4 overall in the 2021 MLB draft out of Eastlake High School in Chula Vista, Calif. He quickly became one of baseball's Top 100 prospects as he worked his way up the Red Sox system.

When Boston promoted him in May of 2025, he was a .300 hitter. For his minor league career, he slashed .273/.360/.466 with 46 home runs and 205 RBI.

The power he showed in the minor leagues hasn't yet translated to the majors. The wrist injury he suffered in 2025 required surgery. The ulnar injury earlier this season sapped is power. The Giants aren't expecting Mayer to be a 20-home run hitter. But they would like him to become a consistent 10-to-15 home run hitter, especially since he has the potential to hit for such a high average in the Majors.

He got in some live batting practice with the Giants on Friday. San Francisco hopes to see him in the starting lineup soon.

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