Hi Lisa! Good that you got him in hospital tank set-up. Can you take him to Vet for X-ray? That would positively ID or rule out a physical injury and it's what I would do. Other than that is to keep him in hospital set-up and hope he recovers by itself; but if injured and without Vet care that leg might be messed-up permanently. Make sure all his "toys" aren't capable of accidentally catching on to legs and cause injuries. Good luck !