WALTHAM, Mass. – Celtics forward Paul Pierce didn’t practice Friday because of a nagging heel injury and might not play in Boston’s opener at New York on Christmas Day.

Pierce did shoot around after the session, but Coach Doc Rivers wasn’t optimistic his captain would be available Sunday, when the Celtics and Knicks play one of the NBA’s five season openers.

“He didn’t do anything,” Rivers said. “He seemed to be working more as far as working out, so we’ll see. I still think it’s doubtful but we’ll see.”

“I think we’ll know better (today). Paul may wake up and say, ‘Coach, I wanna go.’ I can tell you this, it’s very unlikely he’ll start if he plays. I don’t think that will happen. If he does play, he’ll play 15 to 20 minutes, but right now I don’t see him playing.”

If Pierce is unable to go, Rivers said Sasha Pavlovic likely would start in his place.

Pavlovic started the exhibition finale Wednesday night against the Toronto Raptors, when Rajon Rondo, Ray Allen, Jermaine O’Neal and Kevin Garnett also started.

Rivers said he won’t let Pierce’s desire to play override any concerns from the team’s medical staff.

That’s especially important this season with the condensed 66-game schedule expected to take a physical toll on players.

“It’s the medical staff’s decision,” Rivers said. “It’s 100 percent the medical staff. I think this year it’s really going to have to be that because we can’t trust them in that because if they do play and further their injury, and they miss 10 games, that’s (like) 25 games because of the shortened season.”