My first thought was scaly leg before I read your post, still do, but I think bumble foot is a lump underneath. maybe if he is jumping down from a height he may have hurt the equivalent of our ankle? (not up on bird anatomy

).
Go in at night to catch him when they are sleepy, if he is difficult to catch I would keep himin a smaller cage until he has been treated, may also give his foot/'ankle' a rest as well.
Hope he comes right for you.