He landed awkwardly trying to haul in an offensive rebound midway through the first quarter of Game 6 of the NBA Finals on Tuesday night and suffered a right knee sprain.
Perkins was hopeful, saying: "I'm going to try to give it a go [on Thursday]." But a team source told ESPN.com's Chris Sheridan: "He's done."
Perkins underwent X-rays during the Lakers' 89-67 win that tied the series at 3. He suffered sprains to both his medial collateral ligament and posterior cruciate ligament, sources told ESPN The Magazine's Ric Bucher. The team said that Perkins will be re-evaluated on Wednesday, which likely means an MRI to ascertain the extent of the damage.
Boston players also didn't sound very optimistic, bracing for Game 7 without Perkins. But they refused to use his potential absence as an excuse for not closing out this series.
"Perk brings rebounding and defense to the game, and toughness," said Celtics captain Paul Pierce. "We lose that, but that's not an excuse. We're a mentally tough team. We've had injuries all year that we've dealt with. We know how to win when guys go down, so that's no excuse for us."
Added point guard Rajon Rondo: "That's why we have a lot of guys throughout the roster. We have Big Baby [Glen Davis] and Rasheed [Wallace]. Other guys have to step up. We've had injuries before all season and guys have stepped up. I'm sure they'll be up for the challenge and ready to play."
Celtics coach Doc Rivers didn't disclose the severity of the injury or what he had been told, but didn't sound optimistic, either.
"I don't know," said Rivers. "It doesn't look great, but I don't know."
Perkins spilled hard to the floor after being sandwiched between Andrew Bynum and Kobe Bryant as the trio battled for a loose rebound under the Boston basket with 5 minutes, 30 seconds to play in the first frame. Bynum got tagged with a foul for coming in over the top, and his momentum carried Perkins into Bryant.
Dr. Brian McKeon, the team's physician, attended to Perkins during a timeout on the floor and Perkins hobbled off using Brian Scalabrine, Davis, and Shelden Williams as crutches. He went straight to the locker room for further examination.
Wallace took Perkins' place in the lineup. Perkins played the first 6:30, missing the only shot he took.
The Celtics are trying to wrap up their 18th championship, but will have to win Game 7 on Thursday to do so.
Bynum, who has been battling his own knee injury, went to the locker room early in the third quarter.
"[Bynum] wasn't able to move very fluidly the second half," said Lakers coach Phil Jackson. "He had some tightness in the back of his leg. He just said, 'You've got to take me out. I can't run.' And it was obvious at that point that he couldn't. He had some swelling in the back of his leg, and we'll have to work on that and see if they can't ice it down and control that."
Chris Forsberg covers the Celtics for ESPNBoston.com. Information from The Associated Press contributed to this report.