Miller is expected to miss at least a month after undergoing hernia surgery recently, teammate Udonis Haslem revealed Thursday.
Miller confirmed to ESPN.com that he underwent surgery Tuesday.
"I'm doing better," Miller said in a text message. "When it rains it pours. I just can't catch a break right now."
Miller did not attend the first day of unsupervised workouts at the Heat's facility. Haslem said Miller could be out up to eight weeks.
"I know Mike. He's a strong guy, he's going to stay positive and he's going to get back as soon as he can," Haslem said. "The key with Mike is, we've got to fight him not to get back too fast. He's going to want to be out there. He's going to want to play. He's got to just pace himself and get healthy."
It's hard to imagine the surgery coming at a worse time for the sharpshooter. Not only would eight weeks sideline him through the start of the season on Dec. 25, but it could mean his days in a Heat uniform are over.
Under the tentative collective bargaining agreement, teams can use an amnesty provision that would allow the team to release a player and remove his salary off the books. Under the rules, teams still would be required to pay the player's contract, but it would provide salary-cap relief.
Miller was seen as an amnesty candidate for the Heat, because he is owed $24 million in the next four seasons and on the books for $5.4 million this season.
Releasing Miller would free up considerable cap space for the Heat, enabling them to target more expensive players in free agency, which is set to open Dec. 9.
The procedure marks the third surgery for the 31-year-old since the end of last season, and his fourth in the past year.
He underwent shoulder surgery and thumb surgery after the conclusion of the season. He also underwent thumb surgery in the preseason after getting his thumb caught in a jersey in practice. And he was treated for concussion symptoms in Boston last season.
The injury-riddled guard played just 41 games during the regular season in his Heat debut and averaged only 5.6 points, down from his career average of 13.2.
Tom Haberstroh is a writer for ESPN Insider. Information from The Associated Press was used in this report.