Why is one of my meat chicks developing lumps and losing down?

This little broiler is about a week old. He has had major pasty . (a few others had this problem, but I cleaned them up and fixed the temp. They seem fine.) He has a tennis ball sized lump right under his vent (this lump is squishy). This morning I noticed that the down on his face and neck is falling out. (he also has a new hard lump on what seems to be his left shoulder...) He seems to be doing worse and worse. I have already isolated this chick. He has plenty of water and food. I think I will have to cull him, but can you think of any solutions for the future?