Garnett sat out the previous two games because of a left thigh injury and the flu. Celtics coach Doc Rivers had downplayed the severity of the injury and noted that Garnett would have played in Monday's game if not for the illness.
Although Garnett has been dealing with an adductor strain, Rivers said Monday that the center's absence from the team's showdown with the Heat was due more to a bout with the flu. Garnett had been listed as a game-time decision before that contest.
"[Garnett is] sick, really. It's not the injury," Rivers said before Monday's game. "He just has a terrible flu or whatever, and with the injury, we just felt the combination -- it was too much to play."
Boston went 1-1 in Garnett's absence and begins a four-game road trip Wednesday night.
The Celtics also announced Wednesday that they have re-signed forward D.J. White for the remainder of the season.
White appeared in four games while playing on two 10-day contracts, averaging 2.8 points and 1.5 rebounds over 6.8 minutes per contest. The Celtics had to decide whether to sign him for the rest of the year or cut him loose with league rules allowing no more than two 10-day pacts.
ESPNBoston.com's Chris Forsberg contributed to this report.