If you havent already, I'd suggest seeing a doctor. They may refer you to a physical therapist, who can provide you with the proper exercises to strengthen your leg.
As for training...dont train! I hurt my knee while grappling, a few years ago. It sucked, because I couldnt train, and I was walking like I was a 90yo man. As its been said already, your knees play a big part in grappling, and anything else that involves anything other than sitting, so again, take it easy. Go to class, but watch, take notes, etc.