no. 
i really honestly don't. and cp where only one leg is affected (whilst theoretically possible - monoplegia) is vanishingly rare. if his hands and arms are fine and he;s crossing the midline etc, i would pretty much rule it out.
what happens when you hold him up by his hands/ under his armpits?
has he got an activity centre that he sit/ stands in to play?
i'm still pretty convinced that he just has an unusual pattern of crawling, but of course it's impossible to tell on tinternet, and you are obviously concerned, which is a reasonable sign that there might be a reason for concern, and so you need reassurance. (i have been concerned unnecessarily myself though
)
if i were you, i would pop to the gp as you have an appointment, you can ask all the questions that you are concerned about (ask him about cp too, if you like - better fo you to have a face to face chat) ask if physio is necessary or would be useful, but then try to ignore it for another couple of weeks.
have a really lovely christmas and spend lots of time playing with him. (what happens if you'teach' him how to move btw? we taught dd2 to crawl using the stairs. i would kneel behind her and weight bear for her, and i would alternately move all four limbs in proper crawling fashion up one stair at a time. (she couldn't weight bear on the flat, but could take a little weight through her arms if she was more upright on the stairs, with me helping) the physio thought i was crazy. i would make her do it several times a day. 
i put a toy on the next step up, so it was just play-physio really. 
and eventually she did crawl, in proper reciprocal fashion. not all babies do though. you might just have one that doesn't. 