I'm not a super expert in this, but not sure who else is on right now, so I'll respond.
Looks like he lost a bunch of feathers and section of skin.
I think your rooster has an excellent chance of recovering from this, if you're willing to treat him. Or you can put him down. That's a large section of missing skin, so recovery may take a while. He'll need to be isolated in a clean environment where he can't get dirt into his wound.
I had a chicken who got her skin sliced over her rear and it gaped about an inch wide, but eventually scabbed over and healed. Also, I had a chicken who lost a portion of the skin of her wing on her elbow, which also scabbed over, and then the feathers grew back.
In your case, clean the wound with something - Hibiclens maybe? Rinse it well, distilled water if you have it, saline spray would be even better to reduce pain. Alcohol can be used, but it will sting, so not sure how well that will go over. Soap and water also can be used, just rinse well. Get all debris out that you can see, including anything that slipped between his skin and muscle. Once it's clean, pat dry with clean towel and then apply original Neosporin all over (not pain relief version - caine drugs are poisonous to chickens). Apply Neosporin twice a day until healed. If it starts going in the wrong direction, you may need a systemic antibiotic (pill by mouth). A vet can recommend, or there's some guidance on this site. You might could try and stich some of the skin to itself, if there is a flap, to keep it in place, even if it doesn't totally cover the wound. Make sure to sanitize your needle and thread.
ETA: x2 what
@Wyorp Rock said. They've got more experience with these things than I do.