It's hard to tell from pictures on the internet, but my first impression is a crush injury of some kind. Did the crestie accidentally get its foot closed in a cage door, or could some decoration have fallen on it?

I'd recommend a visit to the vet. A vet could take a closer look and recommend treatment. If that were my gecko, I would take it in to be seen. Be sure to use a herp vet, not a dog and cat specialist.