Butler favored his back after a hard fall on a missed driving layup early in the first quarter. He scored just 10 points on 13 shots before heading to the locker room midway through the third quarter. He did not return.
"He drew contact and got shoved and landed on his tailbone again,'' Heat coach Erik Spoelstra said after the game. "There could not have been a worst scenario for us to start the game. It is a contact sport. It's an unpredictable thing. Insult to injury, we didn't get the call on that either.
"But he definitely re-aggravated it. You can tell from that point on he was not his usual self. So we'll reevaluate him [Tuesday] and see where we are.''
The Heat on Tuesday ruled Butler out for Wednesday's home game against the Milwaukee Bucks.
Markieff Morris also was ruled out for Wednesday's game, which will be the 16th consecutive he will have missed because of a neck injury.
Meanwhile, All-Star big man Bam Adebayo expected to miss four to six weeks after undergoing surgery to repair a torn ligament in his right thumb on Tuesday.
The Associated Press contributed to this report.