Could be any number of things, we recently had a member with what seemed to be a cancerous growth on a chicken. Might be an infected cut, is he fighting with other roosters? If this is the case you can probably wash it with peroxide and open it up to allow the infection to drain. Gob it with some type of antibiotic ointment. Don't know about ticks, probably not a factor. There are a few types of parasitical worms that grow under the skin of various animals, it would be uncommon on a chicken, but?