Beckett exited Tuesday's start against the Tigers in the third inning with a back spasm.
"He's a little stiff. You know, not surprisingly," said Red Sox manager Bobby Valentine. "He had spasms and he's a big guy, so we don't know how to read that other than it doesn't seem -- when [general manager] Ben [Cherington] talked to him, he said it didn't seem like it was a 15-day stint or anything. It's one of those -- we'll just play it by ear."
Beckett's next turn in the rotation would be Sunday against the Twins.
"I don't know about that even," Valentine said. "The surety of that, I haven't talked with Josh. It will all be predicated on the bullpen session, which isn't until at least tomorrow, maybe the next day, where he'll test it and that will predicate whether he makes the start."
The Red Sox are fortunate in that swingman Franklin Morales can be on standby. Morales pitched out of the bullpen Tuesday, but Valentine will try to stay away from him the next couple of days as Beckett's status is re-evaluated.