I'm assuming that you mean you took him to the vet as you said you got him "back home".
Did you take him to the vet already? If you haven't then get him to 24 hour vet or vet ER asap. There could be major damage or at least pain. He needs to be eating and drinking and he could even have damage that causes internal bleeding. He could have a variety of illnesses from the bites, He could have serious tissue damage. It's hard because they have so much hair so your can't see the injuries well, and they obviously can't tell you how they feel. You need to take the lack of appetite as serious, not just a sign of "depression" or shock.
If you did take him to the vet: Is he doped up from pain meds or surgery anaethesia? If he's not eating, you need to call the vet and get him in for an IV for fluids. Don't put that off. If he had a mouth injury, he still needs fluids even if there's pain. With injury in that area, you'll need to ask the vet about some kind of way to get food into him. If your dog is running a fever or vomiting, etc, he's probably fighting an infection from the attack and that would mean he needs antibiotics asap. He wouldn't be all that hungry and the vomiting or fever would mean he needs rehydration asap as well.