Tristan Thompson, a member of the Cleveland Cavaliers the past nine seasons, has been unable to practice since signing with the Celtics because of a hamstring injury. Nick Wass/Associated Press

For now, Tristan Thompson’s greatest challenge appears to be getting on the floor before the Boston Celtics’ Dec. 23 season opener against Milwaukee.

Celtics Coach Brad Stevens doesn’t know if his new big man will recover on time from hamstring trouble to be available on opening night.

“I think that’s hard to say right now. He’s not been in any part of practice yet. He’s done our pre-practice, similar to (Kemba Walker), like a 2-on-2, 3-on-3, very light, simulated reads work on both ends,” said Stevens. “So that’s it. So he hasn’t played in a long time, he didn’t play in the bubble, so there will be a ramp up period for him whenever he is able to go live in practice, and I’m assuming it won’t be just one of those situations where you’re available one day and you get a good practice in and you can play.

“I think it’ll be a little more than that. I don’t know what that means with regard to Dec. 23. Every day that passes, I’d say that becomes more unlikely.”

Rookie point guard Payton Pritchard was another casualty at Saturday’s practice, with a dislocated finger.

“Payton Pritchard had his finger pop out. I don’t know what the right medical term is for that,” said Stevens. “But they were able to place it back, and hopefully his timeline to return to practice will be sooner rather than later on his left hand. But I think everybody else has been good to go.”

Though still strengthening his knee, Walker has started the light workout part of his rehabilitation.

“He does individual shooting, mostly spot shooting, a little bit of movement, but that’s it,” said Stevens. “Nothing with the team, nothing in small groups, just 1-on-1 with a coach.

“I really haven’t even asked,” Stevens said when asked if Walker has a new timeline for return. “I’m going to learn more in early January about real timelines. I’m guessing like everything else, he’ll probably progress to the next stage fairly quickly. Next stage might be like being involved in a four-person group work where you’re doing some simulated defensive drills or simulated offensive reads, oftentimes not going full speed.”

BROWN IMPRESSES TEAGUE: Jaylen Brown, as one of the league’s great young voices, didn’t need long to win over Jeff Teague.

“He’s one of our leaders in the NBA, man. Off the court, we all know what he does, what he brings to the table, his voice, his activism,” said Teague. “He’s a talented player and a talented person off the court. He’s got a great heart, man.

“When I first got here, he was the first guy to call me and tell me, if I needed anything, he’d show me around the city and let me know anything. That’s just the kind of person that he is. And since I’ve been here, he’s texted me every day, seeing if I was cool, if I needed anything, where to go to eat, what’s a cool spot to order in from, and things like that. So that’s just the kind of person he is, and I think we all know that he’s a special person.”

Indeed, Brown is also settling in nicely as a local leader – in Boston.

“It’s great. I’ve been in Boston for five years, and I’m a Bostonian now in a sense,” said Brown. “It’s a major time of my life I’ve spent in Boston now. I’m trying to be a part of the solutions and not the problems here, and trying to see where I can help out, because it takes a community, and I’m trying to be a part of this community. Definitely trying to get more engaged and seeing where I can help out the most.”

PRESEASON OPENER: Though Tuesday’s exhibition opener in Philadelphia will arrive in the blink of an eye, Brown thinks it will find his team restless.

“I think we’re ready to come out and throw a couple of punches, get things started,” he said. “We have a lot of young guys excited to play. Guys like me who are excited to get back out there, too. We should be good. I think we should be ready to roll. Obviously we have a new team, filling out some chemistry, building some new chemistry, starting out with Jeff and Tristan when he comes back. But I think we should be ready to roll.”