BALTIMORE -- Red Sox right-handed rookie Richard Fitts left Monday's game against the Orioles during the sixth inning with right biceps tightness.

Fitts looked down at his arm after throwing his first pitch in the sixth inning, a 94.2 mph outside fastball to Coby Mayo. Manager Alex Cora and head athletic trainer Brandon Henry rushed to the mound and immediately replaced him with lefty Steven Matz.

The 25-year-old entered the game in the second inning, replacing opener Brennan Bernardino who pitched a scoreless first inning. Fitts allowed three runs on two hits, one homer and three walks while striking out six in 4+ innings. He also hit a batter.

He's 1-4 with a 5.00 ERA in 11 outings (10 starts) this season. Boston acquired him from the Yankees in the Alex Verdugo trade Dec. 5, 2023. Earlier this season, he spent 40 games on the injured list with a right pectoral strain.