It's difficult to know if this is new and ongoing or old, but it wouldn't hurt to treat it anyway.
Buy some Betadyne and some chlorhexidine. Mix a tiny bit of Betadyne in a tiny bit of water (half and half) then dip a soft bristle tooth brush in the mixture. Scrub the spot with the solution until you're sure its very clean. Then rinse it off. Dry it well. Dab on a little chlorhexidine and leave it to dry. The next day, rub in some athlete's foot cream, and continue the foot cream daily until the spot is gone.