Depends.

If scales are missing or broken, it's an injury. If they aren't and are discolored, it's scale rot.

And either way, dab neosporin on the spot daily, don't get it in the snakes eyes, though. After 1-2 sheds it should clear up.

If it starts swelling with fluid after you begin neosporin treatment, it's scale rot. Continue treating and hopefully it will clear up in a shed