Forte confirmed Friday, via the Chicago Sun-Times, that the injury is an MCL sprain, the "same injury" he had in 2011.
Filling in for Forte, Langford impressed with 142 yards from scrimmage on 21 touches in Chicago's Week 9 victory at San Diego.
"He's dual-purpose," coach John Fox said after the game. "He can catch. The catch he made on the 'go' route -- wide receivers have a tough time on that catch. He's explosive. He can take short runs into longer runs. I thought he had a great night."