White fluff on tropical fish.?

I recently bought five neon tetra fish. One has stopped swimming with the other and has two, white, fluffy looking lumps on his sides. I'm not sure what this is, and I'm afraid it might be neon tetra disease. It could also be white spot, but he's not rubbing or itching against anything. Any help on this would be good, so I can decide whether or not to isolate him.
Forgot to add: He's not eating.