Do you know how or when this happened ? For now it's not in bad shape but you want to watch carefully that it doesn't continue up the tail any further. There may be an infection under the scales so you can apply raw [ unpasteurized ] honey or Neosporin to it. If you keep him on a loose substrate get rid of it right away so nothing sticks to it. He should be O.K, just watch it though.
Can you post a few pics of him as well as his tank ?