I'm still pretty new to American Toads but from what I've read they are pretty resilient. I would say to leave him alone as much as possible to avoid any more stress (besides feeding). I would also read the care article here on these toads as well. Of course the best thing would be to take him to a vet but besides that I think you just have to see if he pulls out of this and heals himself. Keep a moist area close to him if hes having a hard time getting to water.