That is obviously sore looking, probably inflamed and swollen too. That hammie must be in a fair amount of pain or discomfort

Looks to me like a skin infection of some sort which will require antibiotics and possibly a cream.
You can buy baytril online but you should never give medication without knowing th correct dosage. In a hamster of that size, i would say no more than 0.1ml once or twice a day but i'm not a vet therefore i cannot say for certain.

Can you get your hands on some vaseline? That may help to soothe the area and prevent a build up of bacteria

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