WALTHAM — Paul Pierce  has participated in just one practice during training camp because of a right heel bruise and with opening day quickly approaching, Celtics  coach Doc Rivers  acknowledged that Pierce may not be ready to play when the regular season opens on Christmas Day against the Knicks.
“I’m concerned not long-term, but I’m concerned short-term,” Rivers said. “We have those two games right off the bat and he’s gone one practice and that’s basically it. So, yeah I’m concerned about it.”
Pierce worked out on Monday while the rest of the team had the day off. Rivers said that his heel was “extremely sore” on Tuesday.
“We just want him to rest,” Rivers said. “The problem with that is, it will be a lot of rest and then he may be ready but with no [practice time], that’s scary and if he’s not, he’s not.”
Pierce won’t play in Wednesday’s final exhibition game against the Raptors and the plan right now is for him to try and test it again on Friday.
The good news for the Celtics is that Sasha Pavlovic  (left wrist) did practice on Tuesday and if he’s able to play, Rivers will have two veteran small forwards with Marquis Daniels  and Pavlovic.
JAJUAN JOHNSON  PASSES THE TEST
Kevin Garnett  has a well-deserved reputation for being hard on young players, but the flip side of that is if the player responds positively to Garnett then there’s nothing he won’t do for him. Rookie big man JaJuan Johnson has apparently received that message.
“Kevin has clearly taken JaJuan under his wing,” Rivers said. “You guys have been around here with Kevin, he gives you the one shot and if he feels you’re paying attention he spends the year with him. JaJuan has obviously passed the test, which is good for everyone because it makes it a bad year for that guy.”
Johnson played just seven minutes on Sunday against Toronto, an indication that he has a long way to go to crack the big man rotation that features Garnett, Jermaine O’Neal , Chris Wilcox  and Brandon Bass . But Johnson has still impressed with his shooting ability and maturity.
There’s a different vibe around the Celtics this season. Aging superstars have been replaced by versatile role players who understand why they’re here and what their job is when they hit the floor.
“Chemistry is phenomenal,” Rivers said. “Continuity’s not very good but really the chemistry, I’ve even heard the veterans talk about how this team you can see that will not be a problem this year but the continuity, that’s going to take some time.”
Rivers credited the veterans acquired to fill out reserve roles for their approach in practice.
“It’s always the problem ‘ role players understanding they’re role players,” Rivers said. “We’ve got a group of guys that clearly know who they are but they’re also very comfortable in that. They think they can play as well as the starters but they accept where they’re at.”
That’s important for this team because the bench was its undoing last season, a fact Rivers acknowledged. (Go here for more on the new-look rotation ).
“Last year we failed miserably. Me and everything. We didn’t do the bench and the bench didn’t save us ever,” the coach said. “It lost some games for us but it didn’t save us in a lot. This bench, the one thing I do like, they’re not going to back up. That doesn’t mean they’re going to play well but I like they’re a tough group. They respect the starters but that’s about it. That’s all they’re getting.”
One player who has particularly stood out for Rivers has been Keyon Dooling .
“I love him. We couldn’t have picked a better guy to back up [Rajon] Rondo  with his spirit, with his knowledge, being a veteran, the fact that he can make open shots and he challenges Rondo every day in practice,” Rivers said. “Rondo has laughed about it several times, ‘This guy doesn’t back up at all,’ and it’s been great. They go at each other in a positive way. I think it’s the first time Rondo’s had that and it’s been great for him.”
ROSTER MOVES COMING?
Rivers said the Celtics would probably settle on a final 15 either before or immediately after Wednesday’s exhibition game. With 13 players on guaranteed contracts, they have two roster spots available. If they stay in-house, big man Greg Stiemsma  and rookie guard Gilbert Brown would probably have the inside track. They could also start the season with one or both spots open and see who becomes available.