Shaquille O'Neal (bruise) day to day

WALTHAM, Mass. -- The revolving door of O'Neals continued Sunday as Celtics starting center Shaquille O'Neal did not participate in Boston's two-hour session due to the bruise suffered near his right knee in Friday's win over the Knicks, while Jermaine O'Neal returned to practice after sitting out Friday's game with a sore left knee.

"The O'Neal brothers are both banged up a little bit," admitted Boston coach Doc Rivers, but he wouldn't tip his hand on how the Celtics will proceed, noting they've got some time before Tuesday's visit to Detroit.

"Shaq, we didn't even think about doing anything today. Our fear, and this is going to happen one day, when we don't have either one of the O'Neal brothers. That would be a concern for us. Right now, I think the way it looks, we'll have Jermaine, but I don't know about Shaq.

"I'm going to let [trainer] Eddie [Lacerte] tell me. I always just wait [for that]. Eddie thought [Shaq] coudn't practice today, even if he wanted to. We'll wait until [Monday to determine if Shaq will practice then]."

For his part, Shaq expressed a desire to be back on the court Monday, but said if he couldn't he'd simply rest. He said he joined Kendrick Perkins and strength and conditioning coach Brian Doo in the pool Sunday, swimming laps for a low-impact activity on the tender knee.

But Shaq didn't lack any of his typical sense of humor. Asked about the injury he noted, "It's a bruise, I'll let you rub it and touch it if you'd like," before bursting into laughter.

As for Jermaine O'Neal, he wasn't in such a laughing mood, despite his ability to go through most of the session. Wearing a brace over his left knee, he said the injury swelled up after Wednesday's game in Cleveland. He also used a word that's becoming common to describe his season thus far -- "disappointing" -- noting that multiple injuries (hamstring, back, wrist, and knee) have kept him from finding any sort of rhythm or comfort level with his teammates.

"My comfort level is at an all-time low in terms of chemistry," admitted Jermaine O'Neal.

Rivers admitted the Semih Erden Era could start in earnest Tuesday against the Pistons, with potential even for Erden to start (he ran with the first-teamers at the end of Sunday's session). That would take some of the pressure off the rookie center, who has yet to see floor time despite being active through the first three games. It would also allow the team to keep Glen Davis in his first-off-the-bench role.

"I don't like starting Baby; Baby comes in at the 5 or 4 off the bench and when you start him, now you really take away a lot of options," said Rivers. "And then if he gets in foul trouble, you've taken away all your options."

So if Shaq can't go, Rivers would prefer to lean on Jermaine O'Neal as a starter, but if the team isn't confident he can perform at a high level, that job might fall to Erden.

Rivers heaped high praise on Erden despite his lack of court time thus far.

"He knows how to play, he's just trying to learn how to play our way," said Rivers. "The language barrier is a problem, no doubt about that, but we just gotta keep working on it. He's going to be a good big in this league and he's going to be a good big in this league for a long time.

"I don't know if he's a good enough big right now. He is talent wise, but there's just so many things. It's tough when you're a rookie and you understand me; it's even tougher when you don't."

Chris Forsberg covers the Celtics for ESPNBoston.com.