Thomas, who earlier in the season was sidelined seven weeks with a broken left forearm, missed Saturday's contest against the Miami Heat at the United Center.
The team did not give specifics on the reason for the suspension.
"It's unfortunate," Bulls coach Vinny Del Negro said before his team's 95-91 win Saturday. "It's an internal matter. [Bulls GM] Gar [Forman] and myself will handle it. We've got to focus in on the game [Saturday night] and try to find a way to play better in the last few games to get a win."
Thomas' suspension was another blow to a team that had lost three straight and was already short-handed up front for Saturday's game, with Joakim Noah sidelined by plantar fasciitis in his left foot that is expected to keep him out until after the All-Star break.
"It's unfortunate timing, but in the short run there's a responsibility," Del Negro said. "No one player is bigger than the team, and there's a responsibility to do things right. And I think by handling the situation the right way, which I think we are, I know we are. It's not one person. It's a group. And you have to be committed to your teammates, your coaches, the organization. That doesn't go just for Tyrus. It goes for everybody. The guys know how things run around here. That's how it's going to be."
Asked about the suspension, Bulls veteran guard Lindsey Hunter suggested the 23-year-old Thomas may still have some growing up to do.
"Life is full of trials and tribulations," Hunter said. "If you get frustrated every time you have [a problem] then you're going to live a pretty frustrated life.
"We all have areas in our life we need to grow up in. As long as you realize it and you constantly work on those things, eventually you conquer your own demons. I think that's a battle within he has to work on."
Thomas is averaging 8.5 points and 6.2 rebounds over 25 games in his fourth season.
Nick Friedell covers the Bulls for ESPNChicago.com. Information from the Associated Press was used in this report