My granddaughter got a Chihuahua puppy for Christmas. He is approximately 1 1/2 months old.Loves to run and play,is still eating and drinking good. Tonight she was playing with Tobi(the puppy),and he yelped. Now he is favoring his front leg while walking.He will move it if he is being held. If he is trying to walk or run he limps,but does now whine or holler. Any ideas what it might be? My daughter is going to take him to the vet tomorrow,I just wondering if anyone had any advice tonight.