Looks like early stages of scale rot, however it could just be dirt or even a small burn. If it doesn't improve I recommend getting some betadine solution (can get it behind the counter at any pharmacy) and do some short soaking sessions (betadine should be diluted with water, where it resembles the colour of tea). You can also use a triple antibiotic ointment to help the healing process.
If it doesn't worsen it should go away once he sheds
just keep him on paper towels until it goes away and make sure the towel doesn't get soaked as too much humidity can create problems.
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