Looks like beginning of a hot spot to me. Im battling one with Addie right now. Search the forum for "hot spot" and you will find great info. Do not let him/her lick it. Buy an Elizabethan collar if you have to.
Edit: Disclaimer- I am not a vet so that is only my personal opinion. I do work as office manager in a vet clinic, but I do not give medical advice. Always best to check with your vet if the spot gets worse or is not going away on it's own