William wouldn't eat either. He was missing for a week, then with the vet for a week and still wouldn't eat when I got him home. He is very timid though and I think was frightened of the change and also they are still in a lot of pain. Have you asked your vet? My vet prescribed an appetite stimulant in the end. It worked like a chemical cosh. He immediately started eating and he didn't need anything further - he just carried on eating on his own after that. Your vet should also be able to provide special food for him.
Best of luck