Sounds like it could be it's mucous coating. All fish have them which is why they feel slippery. Yours may have increased mucous because of stress or injury. there could also be parasites on it's skin so have a close look at it if you can. There is also a disease that makes the fish look like that but I can't remember what it's called It's early in the morning for me
Sounds like what my clown fish had when I first brought it home. For the life of me I can't remember the name of the disease either. Is there anyway we could see a pic of the little guy? I gave mine a FW dip, and it cleared it right up, but I'd hate to tell you to do that if it's not necessary.