Gibson says his leg buckled when he stepped on the foot of Oklahoma City guard Reggie Jackson in the fourth quarter of Sunday's 102-72 loss to the Thunder.
Gibson had an MRI and was diagnosed with a sprained medial collateral ligament. He says doctors are planning to take another look to make sure there are no small tears in the knee.
The sliding Bulls had dropped four of six games heading into Tuesday night's matchup with the Cleveland Cavaliers. All-Star point guard Derrick Rose has been out all season while he recovers from major knee surgery.