Poor little guy!!!!!
I would definately keep him off that leg. I would put moist heat on it and make sure he doesn't walk around too much 2nite. If it is injured, you definately don't want him to injure it more. Also, if it isn't something serious, staying off of it will give him time to recover. Maybe he'll be good as new tomorrow! Hopefully it is nothing serious and just a pulled muscle. ((((((hugs)))))) from Hobbs and Hootie! Let us know what the vet says!