Okay,
Bear with me here. You said you can still see the outline of the scale ? If the scale was truly missing, the skin beneath should be white/cream, not dark.
The photos are a little fuzzy and not really close up, it looks to me like his color changed, not that he lost scales. If you run your fingertip over the spot, is it soft and leathery or can you feel scales?
If you can feel the scales, it is entirely possible that he just changed colors. It happens all the time with ball pythons. If you cannot feel the scales at all, just soft, faintly leathery skin, I would recommend a vet visit to rule out infection.
NEVER home treat anything like this with a unproven method you read on the internet, that is a really good way to get into a lot of trouble.
Gale
