The Red Sox acquired Monasterio on Monday in a trade with the Brewers, Mark Feinsand of MLB.com reports.
Monasterio offers a steady glove at multiple infield spots and he improved offensively with the Brewers in 2025, slashing .270/.319/.437 with four home runs over 68 regular-season contests. The 28-year-old enters a crowded infield picture for the Red Sox and will most likely open 2026 in a reserve role.