Red Hairless Patch On Cats Neck

Hello what could this be? It's under my cats neck. It's very dark red and there is no fur there anymore. is it because of scratching? or is it a pest? He is an indoor cat!

It looks like a wound with a scab to me but it's always hard to tell from a photo. How is your cat generally doing? Is he active? eating ok? Using the litterbox? I'm asking because an infected wound could induce fever. 

If anything is not as it should be, other than the scab, or if this gets worse, I think you'd have to get him to the vet.