PHILADELPHIA -- Celtics coach Doc Rivers said shooting guard Ray Allen struggled to warm up before Friday's game against the Philadelphia 76ers and will sit out due to a bothersome left ankle. Mickael Pietrus will start in his place.

Allen originally tweaked the ankle during the fourth quarter of a win over the Los Angeles Clippers on March 12. Rivers believes the injury has flared because of the amount of activity on this trip.

"[The Clippers game] feels like a month ago, but it’s on this same trip," said Rivers. "Really, I would probably say he had the ankle [injury] and the amount of games after the ankle [injury] probably had more to do with it than anything else...

"[Allen] tried to shoot [Friday], he comes over early, [but he] just couldn’t get shots up. That’s unusual. When Ray pulls himself out, then his ankle is really bothering him."

Allen returned in the final moments after injuring the ankle in Los Angeles in a game in which he played 40 minutes, 21 seconds. He played 169 minutes over five games in the 10 days after the injury, including a low of 25:26 against Milwaukee Thursday night, but the ankle was bothersome enough to force him out of the final game of this season-long eight-game road trip.

The Celtics can take solace in the fact that they are 5-0 when Allen has not played this season, including 2-0 with Pietrus in his place.