Any suggestions about why my dog is limping without any visible issues?

I have a 6 month old Great Pyrenees and for the last 1 1/2 weeks he has been limping on his L front leg. While he was laying down I looked for splinters in his pads, I felt all over his leg & up around his shoulder & he lets me pick it up & feel around & I can even mildy shake it around and he does not cry or yelp or try an bite me. My thought is that he possibly may have a strained muscle or something of that nature. Again he favors it but he doesn't cry or yelp upon putting a little bit of pressure on it but he does favor it. I have all intentions of calling the vet but does anyone have any input. Please help!!