Back issues may prevent Frias' next start

LOS ANGELES -- Carlos Frias' next start is up in the air as the Dodgers right-hander continues to deal with a lower back injury.

Frias had an MRI that showed no structural damage, and he threw a bullpen session on Friday. He's scheduled to start against the Phillies on Monday.

"He was OK today, probably not as quite as good as we would've liked him to be, so we're still talking about that," manager Don Mattingly said. "We haven't really made a decision on him yet. The 'pen [session] seemed to go good, it was better than [his last start], but it still wasn't free and just totally out of his mind. So it's something we're going to be talking about."

Frias has been dealing with lower back stiffness in his past two starts, lasting only five innings in both. Mattingly described the pain to be on the side of his lower back.

"Everything came out totally clean as far as structural problems, but that doesn't mean he's not still feeling something," Mattingly said.

If Frias is unable to go Monday, Ian Thomas could be a fill-in, although Mattingly said that there have been no definite plans made as far as a potential replacement.

Frias, who is 5-5 this season with a 4.39 ERA, hasn't lasted longer than 5 1/3 innings in his past four starts.