Thomas was not at the United Center Tuesday night. Rookie Taj Gibson started at power forward.
Thomas was sent home earlier Tuesday during the team's shootaround with flu-like symptoms.
"Tyrus is sick and he won't play," Bulls head coach Vinny Del Negro said before the game.
Also, the deadline passed for members of the 2006 class to sign extensions with their teams, and Thomas did not reach agreement with the Bulls. He will become a restricted free agent at the end of the season.
Del Negro was asked in the pregame news conference if he has been upset in any way with Thomas' play this season. Thomas did not play in the fourth quarter of Sunday night's loss to the Heat.
"I'm unhappy with our play as a team," the Bulls coach said. "I'm not going to talk about guys individually like that. Everyone needs to pick it up a little bit."