I would assume you could still do most exercises, anything lying down or sitting, maybe you will need to use lighter weights, bigger reps if the leg is unable to offer to much stability action. Targeting the leg may be a hassel, not sure if you can do hammy curls, or leg extension, I would also take this oppertunity to stretch you leg / hip muscles if you cant work them.
I mentioned elsewere swimming will be a great all over exercise, and will really help with aerobic fitness and weight loss.