Is he scratching? If so, it might be mites. But if he's not, it's not mites.
My bet is that it's fungal, maybe ringworm. Go to any pharmacy and get some Nystatin or Lotrimin. Apply it twice a day with a q-tip, and rub it in well. After a few days, compare to the picture and see if it's getting any larger. If not, keep on with the antifungal meds. And keep applying it for 7-10 days after you see the hair starting to regrow. It's hard to get rid of a fungus, so don't stop the meds too soon. Also, wash your hands carefully after handling him.
If it is getting larger after about a week, then switch to a triple antibiotic cream, any pharmacy, apply the same way.
The reason we start with fungal medication is because if it is a fungus, an antibiotic will make it worse. But if it's bacterial, the antifungal ointment won't do anything to it one way or the other.
Post back in a week or so and let us know how he's doing.
just when I thought it was all better 
