Kendrick Perkins, Jermaine O'Neal work

WALTHAM, Mass. -- The
Boston Celtics, who have been juggling injured big men all season, got some encouraging news on Tuesday.

Center Kendrick Perkins participated in his most heightened on-court activity since undergoing offseason ACL surgery on his right knee, taking a big step forward in his quest to return to the lineup later this season.

After an MRI last week, the training staff gave Perkins the OK to attempt non-contact work, and he joined his teammates on the court for both stretching and skeleton work during Tuesday's 75-minute session. Perkins worked with the first team while running some basic sets and capped some pick-and-roll exercises with a series of dunks.

"I went through the dummy offense a little bit with the guys -- got up and down a bit -- it felt pretty good," Perkins said. "We just went over some plays. It was good to be out there."

The team might get more immediate help as well.

Center Jermaine O'Neal went through his second full practice session and estimated he's "50/50" to play in Wednesday's game against the 76ers. He said he'll definitely be back on the court this week.

O'Neal has missed the last 18 games because of lingering left knee soreness that originally forced him to the bench during the second half of a loss to the Dallas Mavericks on Nov. 8.

"I'm still trying to get my cardio and conditioning together," O'Neal said. "I haven't really talked with the [training] staff yet. We're going to talk [later Wednesday]. I'd say there's a 50/50 chance [to play vs. Philadelphia]. At some point, I'm going to play this week, whether it's [Wednesday] or Christmas Day.

"I think I can help the team, but for how long? I don't know," O'Neal said. "So as far as conditioning, I'm going to work out again this afternoon, get on the treadmill, and that would be only a test. The knee itself, it's fine."

Perkins, who got fitted for a new brace last week, said he dunked immediately after trying it on -- "Just to make sure I still can," he joked -- but said he surprised himself Tuesday by not thinking about the injury and moving well.

"A couple of times I did [think about the knee], like on a pick-and-roll that I went up and dunked, but I didn't even think about it then, not until after. I was like, 'Damn, I might be all right, after all.' I felt pretty good out there.

"I guess, basically, it's having the confidence to know that -- you're kinda going to be scared on it the first couple times being back out there -- but [I wasn't] really today. My timing was a little off, but I thought I did pretty well for my first time back."

Perkins said he hasn't experienced any setbacks and simply wants to keep moving forward, but admitted that the coaching staff's goals for his return might be even more ambitious than his own. He said coach Doc Rivers pegged a potential return to full-throttle practice for late January or early February, but Perkins is still eyeing the All-Star break. He'll do more skeleton work for the next month or so, then ease his way into contact drills in the new year.

Rivers stressed that, despite the timeline, the team is tempering expectations knowing how hard it is for a player to bounce back from that surgery.

"The mental part is when he comes back, how much he trusts his leg," Rivers said. "If we can get anything out of Perk this year, we'll be thrilled. I know he's going to play, but it usually takes a year after surgery to be completely confident."

O'Neal admitted he's eager to get back on the court, but doesn't want to rush after all the time he's put into making sure he's healthy. He did say he thinks he could make an immediate impact with the second-unit defense, even after admitting to an up-and-down practice.

He stressed that his conditioning, not the knee, is the biggest concern.

"My body is going to be a little sore, I've been out a month and a half," O'Neal said. "But there's a difference between soreness and pain. I'm just a little sore. This is who I am right now. This is what God has given me right now. You deal with it and move forward. With the brace, it's going to help, but I can't guarantee that the knee is not going to flare up. But right now I feel good, I feel strong, I feel capable of helping the team."

The Celtics just got Shaquille O'Neal back in the lineup after he missed a number of games with a calf injury.

Chris Forsberg covers the Celtics for ESPNBoston.com.