Most states require you to have a wildlife rehabilitator license before you could even take the thing to a vet. The vet, I'm sure, would be required to comply with whatever laws apply - including possibly turning you in. One of those situations where they might not want to, but it's their license to practice veterinary medicine at stake.

Call animal control. It's shaky enough trying to diagnose each other's ailments over the Internet. Trying to do it with an animal that can't speak for itself and of which you've had limited observation ...