It could just be some minor bruising, rather than anything serious.
If you're going to get him, then please do so before he stays too long under less than suitable conditions.
Jackson's are not recommended for people new to chams because they are often wildcaught and less able to tolerate mistakes in care than Veiled or Panther chams are.
If you are willing to setup
everything the way he needs it to be, then it is certainly possible to be successful with a Jackson's.
You can't provide what you think is "good enough", as it won't be.
You will need to be especially careful to give him far less supplementation than other chams require (about 1/2 the calcium, calcium with D3 and multivitamin as compared to Veileds/Panthers.)
A varied diet of gutloaded feeders is also needed.
Forget the commercial gutloads and use fresh veggies/fruits to feed your feeder insects.
Take notice that Jackson's need a surprisingly large cage and plenty of humidity and water.
Many successful Jackson's keepers buy MistKing or Aquazamp misting systems to provide enough water.
Petstores are notorious for selling people what they shouldn't use when it comes to chams.
Here is an excellent caresheet to look over and see what a Jackson's truly needs to live a healthy life:
https://www.chameleonforums.com/care/caresheets/jacksons/
