Your dog could be having some pressure pain. I would watch him and see if he continues to limp. If he does for more than 2 more days take him to the vet to get an experts answer. Good luck, and give him a kiss on the head ti make him feel better :)
there could be something in his paw. check his paw and if there isn't anything in there then feel his leg. he could have broken it, got bit by something, bruised it etc. but if you can't find anything like that then try a vet.