Fox Sports insider and NFL Network contributor Jay Glazer reported that the Bears believe Forte suffered a sprained medial collateral ligament, not a torn anterior cruciate ligament, in his right knee during Sunday's 10-3 loss to the Kansas City Chiefs, according to a league source. Glazer reported the running back could be out 2 to 4 weeks.
Bears coach Lovie Smith confirmed that Forte suffered a sprained right knee but didn't offer up any further details about the severity of the injury.
"We'll just keep our fingers crossed," Smith said. "Hopefully it's not serious."
Forte walked off the field under his own power midway through the first quarter after being hit on the knee during a run for no gain. He was brought to the trainer's table on the sideline for tests and was ruled out soon thereafter.
Marion Barber had 14 rushes for 44 yards in Forte's absence, and Kahlil Bell had 34 rushes on four carries.
"Of course any time you can't finish the game, there's concern, but that's all we know right now," Smith said of the injuries.