Andrew Bynum MRI shows bone bruise

EL SEGUNDO, Calif. -- When it rains it pours, even in sunny Los Angeles.

The Lakers were without starting center Andrew Bynum on Tuesday night against the Houston Rockets.

The Lakers had lost four of their past seven games including their past two in a row at home before beating the Rockets 114-106 in overtime.

Bynum underwent an MRI on Tuesday morning that revealed a bone bruise on his left knee.

The six-year veteran has missed 120 games over the past four seasons because of various injuries. He sat out the first 24 games of this season following offseason surgery on his right knee.

The 7-foot, 285-pound big man had his left knee operated on in 2008 after he missed the final 47 regular-season games and all of the playoffs because of a partially dislocated kneecap.

His current knee injury does not appear to be as serious.

"Structurally, he's fine," Lakers head coach Phil Jackson said after the Lakers' shootaround Tuesday afternoon.

A timetable for Bynum's return is uncertain. The Lakers' next game is Thursday against the San Antonio Spurs, whom Los Angeles trails by 7.5 games for first place in the Western Conference.

"It's going to be a day-to-day thing," Jackson said. "Bone bruises are a little bit difficult to just say when guys are going to come back."

Bynum is averaging 11.4 points, 7.3 rebounds and 1.8 blocks per game on the season. The Lakers are 12-5 since he returned to the starting lineup Dec. 29 in New Orleans.

Bynum was not available to the media Tuesday. Jackson said that after reviewing film of the Lakers' 109-96 loss to the Boston Celtics on Sunday it appeared the bone bruise occurred when Celtics forward Paul Pierce was boxing out Bynum for a rebound.

Jackson was asked if he would limit Bynum's playing time when he returns in the same fashion that the Rockets held center Yao Ming to less than 24 minutes per game before a stress ankle in his left ankle ended Yao's season prematurely in December.

"I watch Andrew's minutes a lot and I'm quite aware that I like him in the low 30s," said Jackson. "Twenty-eight minutes is probably ideal for him. That's going to be maybe a help to help anything that could happen accidentally but you can't tell when an accident can happen out there, when someone can get hurt. But, limiting the time can take the risk out of it a little bit."

In 24 games played this season, Bynum is averaging 24.6 minutes per game and 27.4 minutes in 17 games as a starter.

Dave McMenamin covers the Lakers for ESPNLosAngeles.com. Follow him on Twitter.