The appendage on top of a chicken's head is called the comb, and there are different types - single, rose, pea, walnut, etc. Roosters and hens tend to grab and bite the comb when they're fighting with each other, and sometimes when mating. The result is often tearing, even separating the comb from the head.
Most often, a separated comb will reattach very quickly, and torn combs, though they bleed a lot, will knit back together, but sometimes not. You can try super-gluing a torn comb, but the bleeding has to have stopped before trying to glue it. I've tried super-gluing a separated comb, but it didn't work.
Surgery is always an option, too. Chickens can do quite nicely without parts of their combs. I had a pullet that was constantly picked on by the others because she was lowest in the pecking order and her comb was very large, protruding quite a long ways off the back of her head. It was a rose comb with a long tail like a rooster's. The back part was always getting torn from her scalp. I solved the problem by doing a partial dubbing, and removed the back one-fourth of her comb, making it flush with her head so her enemies wouldn't have anything to grab hold of.
If your rooster has part of his comb torn, and it's hanging by a thread, you can go ahead and cut it all the way loose. Put flour on it to halt the bleeding. He will be fine without it. But this is a shot in the dark because you really haven't told us much about the wound, and just what it involves. A photo would be a huge help.
