Heat coach Erik Spoelstra said Haslem missed the team's morning shoot-around to deal with the illness. Rashard Lewis was slated to start in Haslem's absence Monday.
Haslem started the previous two games for the Heat, who turned to the 10-year veteran to help shore up a struggling defense that is ranked among the bottom third in the league in overall efficiency.
"(Haslem) was trying to come out here, but he has not eaten in a day," Spoelstra said. "We're locking the doors (to the arena) so that he doesn't come in."
The Heat have changed their starting lineup four times in the past seven games because of injuries, illnesses or to address defensive concerns.
Haslem has averaged 3.8 points and 4.9 rebounds in 17.8 minutes this season, mostly off the bench. He moved into the starting lineup when Shane Battier recently missed three games with a sprained knee ligament.
The Heat also were without reserve guard Terrel Harris on Monday because of the flu. Haslem and Harris join LeBron James and Dwyane Wade among players who have been limited by the virus at some point this season.