It is a good idea to keep him indoors for sure. My main concern is that you monitor him and make sure he can urinate. If he has any trouble at all, makes frequent trips to the box, lets out only small amounts or starts hiding, get him seen right away as this can be a urinary infection.
If he has sustained an injury, such as a cracked or bruised rib, you are correct that the vet will not splint it or anything, but he could prescribe an anti-inflammatory or pain med to help him feel better while he heals.
For today, be sure he is eating close to his normal amounts, (even if you have to coax him) because lack of food can cause liver problems. He is likely in a good amount of pain if he is not eating...so if you have the means, and ER vet today might not be a bad idea.
I would definitely have him seen tomorrow though, so that you can find out if he does have an injury or a bladder infection, and so that the vet can prescribe something to ease the pain (if it is an injury) so that he will want to eat on his own. He will also be able to determine if there is any sort of internal injury.
I hope this helps! Please let me know how fou fou is doing okay?