Celtics General Manager Danny Ainge said that whether Shaquille O'Neal returns for the regular season or waits until the playoffs is uncertain.

Ainge watched O'Neal go through a private workout at the Celtics practice facility on Wednesday. O'Neal is trying to recover from a sore right Achilles tendon.

"It could be a week or two weeks," said Ainge. "I watched him work out, and he’s starting to do things on the court. We’re just still not sure of when he’s going to come back."

Jermaine O'Neal rejoined the Celtics on Monday following two months on the shelf after arthroscopic surgery on his left knee.

O'Neal could play as soon as Thursday at San Antonio, but Doc Rivers wouldn't commit to that plan.

Danny Ainge's son Austin is the head coach of the Maine Red Claws of the D-League.

“I love the game and the team atmosphere,” Ainge said. “It’s fun to be with a group of guys trying to accomplish a goal.

“There is stress, pressure, joy, failure and disappointment — all the emotions I don’t think you don’t feel quite as intensely as in a regular job.”

Ainge is just 27 and was named Maine's head coach in 2009.

“I feel like I’m learning a lot,” Ainge said. “I get a chance to coach multiple teams — different teams — during a season because of all the roster fluctuations.

"I coach small ball. I coach big guys. I coach slow. I coach fast. You learn to adapt to your personnel. It’s a great environment for a young coach.”

Former Utah Jazz assistant Gordon Chiesa is the NBA’s mentor for D-League coaches.

Ainge is “learning his craft and doing a good job,” Chiesa said. “He’s what I call a new-wave communicator.

“When you’re 30, you communicate with players differently than older coaches, and that’s a positive.

“He’s what the D-League is all about.”

Boston coach Doc Rivers admitted he's heard discussion among his players about Shaquille O'Neal potentially being ready to play part of the Celtics' upcoming four-game road trip.

But Rivers said he actually believes April 5 is the most likely date to expect the Diesel out of the garage.

"[Shaq coming on the road trip is] a possibility, I actually heard that there's a chance, but I don't expect it," Rivers said before Saturday's practice at the Sports Authority Training Center. "I can tell you I've heard different things. I just think that's too optimistic, in my opinion, just being around the game long enough to know that, when they take the boot off, you usually don't play a day later. And I don't see him flying on the plane, getting the boot off -- I just think that's unrealistic.

"There's a better chance -- when do we come home, next Sunday? There's a better chance there [versus Detroit] and I actually don't think that's realistic. It's more likely the game after that [versus Philadelphia]. That would be our target date for Shaq. And I don't even know if that one is [going to hold firm]."

A Celtics team source on Wednesday said that Shaquille O'Neal is mending and on schedule for a return by April 1. That would give him two weeks to get reacquainted with the teammates he left -- and acquainted with the five new teammates with whom he has yet to play.

The Celtics have been understandably cautious in bringing back O'Neal, who, because of his age (39) and his girth (substantial), is not the best candidate for the type of injury he has. Achilles injuries can be notoriously slow to heal for even the most well-conditioned athletes.

Under the scenario outlined by the team source, O'Neal would be back probably by the April 3 game against Detroit. He would thus be back in time for the games against Chicago (April 7) and Miami (April 10), both of which are on the road.

That would be huge for Rivers, who, being a coach, won't allow himself to think such happy thoughts. But the return of Shaq would solidify both the starting five and the bench.

Danny Ainge watched Jermaine O'Neal work out in Chicago this morning, and later said that O’Neal’s return to the team appears to be on schedule.

“It could be next week, which is about what we hoped for - the end of the month,” said Ainge. “He looks good. I watched him go through his workouts.”

The most encouraging news, according to Ainge, is that O’Neal has been able to work out for approximately three weeks without swelling. In addition to working out with a trainer, the center has been playing 1-on-1 basketball.

Ainge said that O’Neal may join the team when it begins a road trip this weekend with back-to-back games in Indiana and Minnesota, though it’s unlikely he would play in either game.

But the trip continues with games in San Antonio (March 31) and Atlanta (April 1) - possible targets for an O’Neal return.

Knowing in the back of his mind that every win is precious in a race for the top seed in the Eastern Conference, Celtics coach Doc Rivers leaned heavily on an eight-man rotation for the second consecutive game as the Celtics rallied from a 15-point deficit to defeat the Knicks Monday Night.

Boston's coach knows he needs to limit minutes for his starters, but must weigh the risk of losing games while battling the Chicago Bulls for the top seed in the East.

Rivers wants to get that eight-man playoff rotation floor time in order to develop much-needed chemistry, but he also needs to get Celtics on the end of his bench acclimated so that he has the faith to call on them over the final 13 games.

Boston has been flat out of the gates in each of its last four games, trailing by a combined 28 points after the first quarter and staring at double-digit halftime deficits in each of their last three contests.

That's forcing Rivers' hand, not allowing him much room to experiment with the new faces.

The Celtics have not been approached by Tennessee about interviewing assistant head coach Lawrence Frank.

“All I know is that Lawrence is under contract with us for the rest of the season,” Danny Ainge said on Wednesday. “Right now he’s committed to helping us win our next NBA title this year.”

Frank's name was floated on Tuesday as the front-runner for the position.

The Celtics have offered an extension to Doc Rivers on multiple occasions, but he has repeatedly said he prefers to wait to make a decision until after the season.

Frank could presumably be a candidate to replace Rivers should the current head coach not return.

Lawrence Frank is the front-runner to become the next head coach of the Tennessee Volunteers, according to sources.

Other candidates include Shaka Smart, Chris Mooney, Anthony Grant, Buzz Williams, Gregg Marshall, Mark Turgeon and Chris Mack.

Adrian Wojnarowski reports that Frank turned down Big East overtures in the past year. Frank was an assistant coach at Tennessee for three seasons under Kevin O'Neill.

Frank is currently an assistant coach with the Celtics.

Jeff Green will give the Celtics every chance to re-sign him, according to his agent, David Falk.

Green will be a restricted free agent this summer.

After a month in Boston, Green is getting accustomed to the atmosphere and appears comfortable enough to make a long-term commitment.

“First of all, I have a very longstanding friendship with Doc [Rivers] and Danny [Ainge],’’ Falk said after the Celtics beat the Knicks, 96-86, last night at Madison Square Garden. “You got a championship-caliber team, three Hall of Famers and [Rajon] Rondo really coming into his own.’’

The CBA expires June 30 and it’s unclear what rules will be in place when the Celtics and Green are allowed to negotiate.

“There’s a lot of uncertainty because no one knows what the rules are going to be, so I told [Green] I don’t want him to spend one nanosecond thinking about next year,’’ Falk said. “I want him thinking about how he can help the team be a factor in the playoffs. And I think he needs to take the next 30 games to get acclimated, learn the plays, get to know how the guys play and I think he can help them in the playoffs.’’