Defensive lineman Israel Idonije also went on IR on Wednesday because of a foot injury.
Tillman, who ranks second in the NFL with six forced fumbles, was injured during the Bears' 36-30 overtime victory over the Minnesota Vikings on Monday night. He broke his ribs and suffered a bruised lung on a helmet hit from teammate Craig Steltz as they tried to tackle Vikings tight end Visanthe Shiancoe on a catch.
Tillman was hospitalized after being transported off the field on a stretcher.
To fill the voids, the Bears elevated quarterback Brett Basanez and cornerback Woodny Turenne to the active roster from the practice squad.
The Associated Press contributed to this report.