Kendrick Perkins is expected to miss two to three weeks with a sprained left knee.
Perkins, who can be a free agent this summer, was unable to agree to an extension with the Celtics, who dealt him to the Thunder at the trade deadline for starters Jeff Green and Nenad Krstic. Guard Nate Robinson also came over to Oklahoma City, which sent the Celtics a 2012 first-round draft pick and cash.
The day before the deadline, Celtics GM Danny Ainge said Perkins would miss at least a week after spraining the medial collateral ligament in his left knee in Tuesday's game against the Golden State Warriors.
"I believe in our medical team," Thunder coach Scott Brooks told The Oklahoman on Saturday. "If they feel it's two to three weeks then I'm comfortable with that. I just want to know when he comes back he's ready to play at the level that he's able to play at."
Perkins was wearing a sleeve on his sprained left knee during his first practice Saturday and said he's hopeful he can be back in time for the Thunder's six-game homestand that starts March 18.
"I'm just here for the long haul," Perkins said. "As long as I can get me some good games in in the regular season, get a good push going into the playoffs, I think I'm going to be all right."
Information from The Associated Press contributed to this report.