Foot Problem

[JANEVANS02]

I have two zebra finches in a cage which I hand reared last September, the plan was to put them in my outside aviary when the weather settles, however recently one of them has a bad foot, I am not sure how to describe it firstly it started by her holding the foot up and on examination it was a little swollen and scabby so I have been bathing it in TCP but it is not really getting any better.

Can anyone tell me what it might be and how to treat it please.