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I am sorry your little one is not well.
Cats can get arthritis however this is more often seen in older cats or as a result of old injury.
It is possible he has injured the paw in some way. Check the paw well in between the pads to look for any splinters, thorns or injuries.
I would just try to rest him for a few days try to limit his activity if possible no jumping or running for 7-10 days. You can see if he will allow you to hold a warm compress on the paw to see if that helps. Massaging is ok as well.
If he continues to limp I would suggest having him seen by the vet.
I hope your boy is ok,please reply back if you have additional questions or concerns
The fact that this kitty is an outdoor kitty I am more suspicious that this is injury related. If he has an injury to the neck this can cause problems in both front legs.
If he is a normal prowler it could be due to a fight (feel the legs for any lumps or healing wounds, he could have been hit by a car or injured by another animal or human.
It really would be best if he was seen by the vet.
Arthritis does not show up suddenly and I really do not think weak bones are the problem.
If you can not have him seen he really should be allowed to stay in the house until you are sure he is ok.