Boston Red Sox president Larry Lucchino announced via Twitter on Monday that right-hander John Lackey has a right biceps strain and there is no structure damage to his arm.
Lackey, who had not pitched in almost 1 1/2 years, left Saturday's game against the Toronto Blue Jays in the fifth inning after hurting his right arm following a pitch.
The 34-year-old last pitched in September of 2011. He was coming back from Tommy John surgery. It was feared that he may have re-injured his elbow, but an MRI revealed no damage.
It is not clear how long Lackey will be out. Alfredo Aceves, who relieved Lackey, is a candidate to fill his spot in the rotation. Prospect Allen Webster and knuckleballer Steven Wright are also possibilities.