Friend, in response to your question I would strongly recommend a hands on examination with family. He will need to be started on prescription pain killers and antibiotics. Do not give over the counter pain killers, they are all toxic to cats. In the meantime this is what you can do to treat the wound:
1- Need to stop him from licking or he is going to delay healing and promote an infection. Pick up an ecollar (cone) in your local pet store to stop him from licking/gnawing at affected area.
2- Pick up in your local pharmacy "Hibiclens" antimicrobial soap or chlorhexiderm scrub. Dilute 1-2 tablespoon for every cup of water. Use this mixture to flush the wound 2-3 times a day. If you do not find this antimicrobial soap flush with plain water.
3- After flushing affected area as above apply a topical antibiotic like neosporin or bacitracin. Then, apply a light bandage over the wound. Place a gauze with antibiotic as the first layer then secure it with gauze tape (do not put it too tight). Do this 2-3 times a day for the next 7-10 days.
4- Follow up with your family veterinarian.
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