The team said Kanter, who is averaging 14.4 points and 6.7 rebounds in just 21.6 minutes per game, will be re-evaluated in about four weeks. League sources told ESPN's Royce Young on Thursday that hecould miss up to two months.
Kanter, who had slapped the floor in frustration a few minutes earlier, walked to the bench during a second-quarter timeout and slammed his fist into the padded chair. But as he brought his arm down, the folding chair flipped up slightly and Kanter caught his right forearm on the metal edge. He quickly went back to the locker room for X-rays, which confirmed a fractured ulna.
"It's tough, man, especially to do it the way he did it -- it's very unfortunate," Russell Westbrook said. "He's a strong man, and he'll be back better.
"Things happen. If he could take it back, he definitely would. But I think now we have to look forward and try to figure out what the positive things are and get him back as soon as possible."
With Kanter out for an expected extended period, the bench will have to rework its identity, probably around guard Cameron Payne, who recently returned from a broken foot.
"Everybody's got to step up, everybody on that second unit, everybody on the team period," Payne said Thursday night. "We all got something we're good at. Enes was great. Enes, what he does in the post, he opens up the floor for everyone, but now everybody else has to bring it every night. Whatever they do well, be great at it. I feel we'll do a pretty good job."
The Thunder sit at 28-19, sixth in the Western Conference and jockeying for playoff seeding.
ESPN's Royce Young contributed to this report.