That looks a lot like something Finn had on his neck once. Was it sticky at all? The one on Finn's neck was a circle like that, and his fur was stuck to it. When I washed it out with a warm wet washcloth, it "ungunked" the fur and revealed that it was a little red circle. It wasn't raised a lot, but it was not flat or recessed. Tiny bit bumpy and a little bit raised. It was bright red like that. It was there for a week or two, but has been gone for awhile. I still don't know what it was, but it never bothered him. If I see anything like it again, he'll go to the vet. It did look a lot like Chipper's spot.