It's good you'll be calling the vet. It could be a bacterial skin infection, or a fungal infection like Ringworm, as you suggested. But it could also be a host of other things.
Your vet will probably give Cooper a good physical examination and perhaps do a skin scraping to look at under the microscope. It could be an easy fix with a topical ointment, or maybe antibiotics or antibacterial shampoo. Whatever the cause, I hope the irritation goes away quickly and isn't too unpleasant for Cooper. You didn't mention whether he's fussing with the rash or not, but if he is try to discourage that.
And I guess Cooper may need to be brushed and combed more regularly, you said he was very matted? He may be going through the dreaded coat change right now and you really do have to stay on top of that. I'm sure you're doing all you can to see that he's comfortable. Good luck and please let us know what the vet says.