Hi there
As a vet, I have to ask, has it had any injections around that area, looks quite localised, and like you said, with only one affected it's a bit less likely to be scab, but best to get it checked out just in case.
Sometimes an individual will react to what they use to preserve injections, so it might be an individual reaction.
Hopefully your vet will be able to tell by looking, touching and skin scraping it, as hard to be sure just from a photo.
Best of luck
Suzanne