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
![Smiley :)](https://www.accidentalsmallholder.net/forum/Smileys/default/smiley.gif)
).
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.