Rooster with fluid filled greenish blister on leg

[CartierChicken]

Yesterday I noticed that one of my young Yokohama roosters had a light greenish colour on one leg. Today the greenish area is full of fluid. I disinfected it. The leg does not feel hot. But to be on the safe side, I gave him a small dose of antibiotics. What could this be? None of my other birds have this.

 

[Mahonri]

did you drain it?

 

[CartierChicken]

Quote:
No. I was not sure if I should, plus I don't know how to go about it. I was hoping to hear from some here about it.