Red Sox Trade Marcelo Mayer to Giants, Full Deadline Deal Revealed in MLB Rumors

The San Francisco Giants acquired infielder Marcelo Mayer from the Boston Red Sox just before the 2026 MLB trade deadline on Monday, according to Joel Sherman of the New York Post.

Boston received relief pitcher Erik Miller in the swap, per Sherman.

As for Mayer, the No. 4 overall pick in the 2021 MLB draft will be experiencing a change of scenery for the first time in his career.

He's appeared in 70 games this season, hitting .220 with three home runs and 10 doubles to go along with 22 RBI.

Mayer's potential was high upon making his Red Sox debut, as he was listed as the No. 12 overall prospect among all teams in 2025 (via MLB.com).

He's been hampered by injuries throughout his two years in the majors, though.

Mayer dealt with a wrist issue that required season-ending surgery during his 2025 campaign. This year, he hasn't played since June 25 due to a bone stress reaction in his left forearm.

The Giants will hope that he can blossom into a key piece of their lineup moving forward, as they currently sit at No. 4 in the National League West standings with a 47-65 record.

As for the Red Sox, they obtained Miller as they look to make a postseason run.

The 28-year-old owns a 2.76 ERA in 38 games this season, racking up 45 strikeouts in 32.2 innings of work. Miller has also limited opposing hitters to a .198/.333/.293 slash line.

Boston boasts a 60-51 record, currently holding the second AL Wild Card spot.