could be Scaley Leg mites..how are the legs? are they scaley or crusty or look rough?
could be exposure to some irritant..such as walking on cement..
could also be a vitamin deficiency..
what all do you feed?
try and get him some poultry vitamins..ASAP..
if you can't get them quickly..you can use Poly-vi-sol liquid baby vitamins, Enfamil brand if possible..no iron..give 2 drops once a day on beak for a week or so,,tpaer off another few days.
in the meantime.try and get the poultry vitamins.
and make up a little of this mixture:
water cooked oatmeal, soft boiled or scrambled egg, plain yogurt..and chicken feed to make mix crumbly..
a teeny bit of lightly cooked liver can be added.
In addition to above, get some Bagbalm (local feed store may have or order on line) and apply daily for a little while. I have had amazing results with regeneration.
JJ