[Plinkploop]

Looks like a scrape in the pictures. Is that a possibility?

*edit- reread your initial post. I do have to say it looks much more like a scrape than a fungus. I'd honestly just keep the water clean and attempt to let it heal on its own for a few days and see how he does.

 

[Plinkploop]

Oh no!! Fingers crossed for the best... You could try pimafix, maybe it's a minor fungal infection?

 

[Plinkploop]

Where there is a fungal infection there is a bacterial infection first. True fungal infections are very rare in the freshwater aquarium. It looks like it may be a scrape or injury that has become infected with bacteria/fungus. The fish still looks pretty healthy: bright eyes, full tummy, no clenching of fins next to body or droopiness of fins ( which indicates weakness). Do you have access to malachite green or methelyene blue? These are the active ingredients in most external parasite meds for Ich. This would be a far better med ( anti-bacterial and antifungall) to use than Pimafix ( an antiseptic with very minimal anti-fungal properties).

I only suggested pimafix because it helped my goldfish that scraped a scale off and got a minor, what appeared to be, fungal infection.