How long has his comb looked like that? Looks kind of like a fungal infection, maybe favus. You might look into that, maybe treat with antifungal (anything mith Miconazole, like athlete's-foot ointment) or Nu-Stock. The latter is good for treating the bare patch as well. It's just a mixture of sulfur, pine oil, and mineral oil, but is supposed to work well on fungus. I used it on my roosters combs and it seemed to clear them up quickly.