"He's feeling OK but really none of us will know for sure until we get back to Miami and we re-evaluate," Heat coach Erik Spoelstra said.
O'Neal was called for traveling with 5:20 left in the quarter and while Bucks center Primoz Brezec was nearby, the two didn't appear to make contact.
The entire team and training staff surrounded O'Neal while a trainer bent and stretched O'Neal's right knee.
After several minutes, O'Neal was helped to his feet and was putting some weight on his right leg. He went to the bench and rubbed the top of his leg with his knee brace pulled down. He did not return to the game.
"When we throw it down to J.O. in the post he kind of settles things a little bit," Wade said. "He's been playing well for us, especially of late. [But] we've played without him before."
The Associated Press contributed to this story.