
The Kansas City Chiefs are fearing the worst with Jamaal Charles, but they are hoping for the best.
According to NFL Media’s Ian Rapoport, the Chiefs fear Charles suffered a torn ACL on his non-contact knee injury Sunday against the Chicago Bears.
The immediate fear is that #Chiefs RB Jamaal Charles tore his ACL, source says, based on initial tests. He'll have an MRI to learn more.
— Ian Rapoport (@RapSheet) October 11, 2015

Charles went down while trying to make a cut against the Bears (video here). Any time a player goes down on a non-contact play it is a serious concern.
Charles suffered a torn ACL injury in Week 2 of the 2011 season. He returned the following year and posted a career-best 1,509 rushing yards, so there is at least a small silver lining if he is seriously injured.