Pomeranz was diagnosed with left triceps tightness, Peter Abraham of The Boston Globe reports.
Pomeranz was pulled from Sunday's start after just three innings. In that time, he'd given up two runs on three hits and three walks. Pomeranz dealt with triceps tightness during spring training but wasn't forced to miss time due to that particular ailment. The team has yet to elaborate on the severity of the injury, but more should be known after Pomeranz has his triceps examined further.