I saw a snapshot of him laying on the ground. It definitely looked like a badly dislocated knee. Reminiscent of Willis McGahee. You could see the end of his femur pushing out (not thru the skin) where the right side of his knee should be with his knee turned to the left clearly dislocated looking.
Given McGahee's return it is possible for him to make it back to football, but it is definitely a potential career ender. I'd imagine it would have to tear the ACL, PCL, and MCL to do dislocate that badly. Not to mention possible fractures and cartilage tears.