Chalmers was hurt on a non-contact play during the first quarter Saturday. He was unable to put weight on the leg as several teammates carried him off the floor.
Chalmers was not available for comment after the game. Heat coach Erik Spoelstra said he was in a brace in the locker room after the game, with an MRI scheduled for Sunday morning.
The Heat called the injury a sprained knee and said he would be re-evaluated on Sunday.
Chalmers has been Miami's starter at the point since Jan. 22, and the Heat have gone 18-9 since he joined the starting lineup. He entered Saturday averaging 6.7 points and 2.4 assists for Miami, which has just one other true point guard -- Mike Bibby -- on the roster.
Also Saturday, the Nuggets lost Arron Afflalo in the first half after he reaggravated a strained left hamstring.
Information from ESPN.com's Brian Windhorst and The Associated Press contributed to this report.