Friend, if the tail is limp is possible he could also have a fracture. Or, sustained enough tissue damage that may have damaged the nerve. Yes, he must be in pain. Unfortunately there is nothing over the counter that can be given to a cat for pain, all of those meds are toxic to cats. He will need to be seen by a veterinarian for a hands on examination, pain medication and oral antibiotics. In the meantime this is what you can do:
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. Do Not let him out with the ecollar on, he must stay indoors.
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 can not find this antimicrobial soap just flush the wound with plain water for a few minutes 2-3 times a day.
3- After flushing affected area as above apply a topical antibiotic like neosporin or bacitracin. Do this 2-3 times a day for the next 10-14 days.
4- Follow up with your family veterinarian.
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