What do you mean by "chomped"? Is there an open wound on him? If you are positive he was bitten / scratched by the cat then you need to get him to a veterinarian immediately.
It may be that he is just too stressed from the cat attack to want to eat right now, but if you keep the lights out and the cat out of the room and he's not eating his favorite treat tomorrow then there's probably a bigger issue as the stress has been gone for 12-24 hours he should be okay by then...