OAKLAND -- Will Middlebrooks, who came out of Sunday's game after suffering a strained left hamstring, was out of the lineup Monday as the Red Sox opened a three-game series against the A's.
Nick Punto was the Red Sox' third baseman.
Middlebrooks, who reported to the Coliseum early in the afternoon to get treatment on the hamstring, said he felt improvement over the day before.
"It's nothing serious," said Middlebrooks. "I'm just having some tightness, soreness. But I don't think it's anything serious. I don't think it's anything to worry about."
Middlebrooks experienced some cramping in the hamstring back in late April and early May when he was first promoted from Pawtucket, but said this was "different."
Asked about a timetable to return to the lineup, Middlebrooks said he wasn't sure, but said he thought it was possible before the trip concludes here Wednesday afternoon.
"They're discussing it now," said Middlebrooks of the training and coaching staff. "I'm just going to wait to hear."
The Red Sox didn't have a player to replace him on the roster present, but manager Bobby Valentine said it was possible the Sox could have someone here by Tuesday.
"He feels better today than he did (Sunday) and better than he expected," said Valentine. "That's the only news we have. It's not discolored and that's good. But it's going to be some days (before he plays). We won't let the calendar dictate; we'll just see how he feels.
"Maybe (a trip to the) DL, maybe a few days. It's just one of those injuries."
Since the Sox are carrying 13 pitchers, they have just three extra position players on the bench -- Punto, Brent Lillibridge and Kelly Shoppach. And with Punto in the lineup and Middlebrooks unavailable for now, Valentine's flexibility is reduced.
"We'll see how he we get through tonight," he said. "I wouldn't be surprised if we have someone here (Tuesday)."
It's possible the Sox could bring in another position player without putting Middlebrooks on the DL. Clayton Mortensen, for instance, could be optioned to Pawtucket to give the Sox another position player for a few days.
"We're trying to evaluate all the possibilities," said Valentine.
Lillibridge has played third before and could be used at the position.
"It's one of the positions he's comfortable with," Valentine said. "I've seen him take ground balls there twice. I think he could play there."