Jon Lester has been placed on the 15-day Disabled List with a strained Latissimus muscle, according to WEEI.com. Lester hurt the back muscle in Tuesday night's 3-2 Red Sox victory over the Toronto Blue Jays, getting pulled from the game after four innings without giving up a hit. He had struck out five and only allowed one base runner in the four innings.
The Red Sox have called up Scott Atchison to take Lester's roster spot.
If Lester returns as soon as he's eligible - a possibility considering such injuries usually take 2-4 weeks to recover and Lester's said that he doesn't consider the injury to be serious - he'll probably only have missed one actual start, with his second start getting pushed back from after the All-Star Break.
The Red Sox are hoping for the quick return, especially since John Lackey continues to struggle and Clay Buchholz is awaiting a third opinion on his own back injury.