"It seems like it's non-problematic," said manager Bobby Valentine on Thursday. "It was a cramp, and he's working out now on the treadmill."
The right-hander was cruising in the game before cramping in the eighth. After getting the first out of the frame, he limped off the mound and trainers attended to him. Beckett stayed in the game and finished the inning. Vicente Padilla replaced him to start the ninth.
Beckett, who declined comment after the game and again on Thursday, had thrown 92 pitches and would have returned for the final inning if not for the cramp, Valentine said.
Despite allowing two runs on five hits, Beckett became the first Red Sox pitcher to lose while holding an opponent without an extra-base hit in an outing of at least eight innings since Frank Castillo on May 22, 2002, vs. the White Sox.
The Sox have lost four games this year when their starters have allowed two earned runs or less. They lost five such games in 2011.
Beckett's gone at least seven innings in each of his last five outings and is 4-6 with a 4.04 ERA in 11 starts this season.