WALTHAM, Mass. – For most of the last three months, Doc Rivers has relayed optimistic reports on Shaquille O’Neal’s recovery from a “minor” injury to his right calf.

One thing the Boston Celtics’ coach doesn’t need to hear from a trainer: whether O’Neal will be any good once he does return.

“He’s still big,” Rivers said before practice Friday. “When he’s on the floor, he’s 7 feet tall — plus — and he weighs what he weighs. Of all the players on the team, he has the easiest task of being who he is. Because that’s all he can be.”

Rivers said O’Neal took part in a limited workout Friday, a day after he ran through some plays and shot baskets while his teammates practiced for Sunday’s opener of the Eastern Conference semifinals at Miami.

Rivers said he’s more confident than ever that O’Neal will play in the series.

“I don’t know when,” Rivers said. “Maybe (Game) 1, maybe 2.”

O’Neal wasn’t available for comment at the Celtics’ practice facility Thursday or Friday. General Manager Danny Ainge said he hasn’t seen O’Neal run, but backup center Glen Davis said O’Neal “looked good.”

“And he says he’s OK,” Davis said. “I’m looking forward to him being back.”

O’Neal signed with the Celtics for the veteran’s minimum last summer, saying he joined Boston’s Big Three for a chance at another title or two before he ended his Hall of Fame career. He played only 37 games in the regular season, and just 5 minutes, 29 seconds since Feb. 1 because of lingering leg problems that have left him perpetually day-to-day.

An injury that originally was supposed to keep him out for a few games has cost him 33 of the last 34 games of the regular season and the entire four-game series against the New York Knicks in the first round of the playoffs. Ainge said O’Neal has been struggling with his downtime and is eager to return.

“I think he was probably discouraged in the New York series. He was really determined to get out on the court,” Ainge said Friday.

“Sometimes the body doesn’t do what the mind wants. But it definitely wasn’t because of a lack of will.”

The Heat are expecting O’Neal to bring his 345 pounds — and six fouls — onto the court for what is expected to be a physical series between the teams that, while not exactly rivals, have plenty of history. Twice in the last three years the Celtics knocked LeBron James’ Cleveland Cavaliers out of the playoffs; last year, that was one round after Boston sent Miami home.

“We don’t know what’s going on there. But obviously it’s a big series for both teams,” said Heat center and former O’Neal teammate Zydrunas Ilgauskas. “So unless it’s something healthwise, I would expect him to be there.”

And health is the only thing that would keep O’Neal away. The team is being extra careful because O’Neal did return April 3 only to hurt himself again.

He hasn’t played since.

“He’s a competitor. He wants to be on the floor to really help that team,” James said. “We’ll see when Sunday gets here and throughout the rest of the series if he’s going to be in uniform. But it doesn’t change our game plan at all.”

When O’Neal returns, Rivers said, he will come off the bench; he wasn’t able to guess how many minutes.

Davis said O’Neal will help clog the lane on defense and bring more playoff experience than the other centers. With four All-Stars already in the lineup, Davis said, “we just need a little bit of offense from him.”

But the good news is O’Neal doesn’t need to relearn how to be tall and strong.

“He has six fouls. He clogs the paint. He’s a big body,” Dwyane Wade of the Heat said. “Of course it’s a positive for them.”