This is a tricky one - and replicated up and down the country. My DS is one of the football crazy boys, and this divide generally works well for him, but it is still there to see even as a parent of one of the 'lucky ones'.
Couple of thoughts: does he want to play football, but he's just not very good/confident? If that's the case, could he do a bit of practising at home/with a few friends etc. In my experience of primary school boys, an awful lot of them see themselves as the glory man up front, and there's definitely more space for more defensively minded players.
If he doesn't want to play, to some extent he's going to have to wait it out. Again, in my experience, the gulf between the very enthusiastic and/or able footballers and the others will widen a lot over the next few years, and more boys who don't get a look in will start to drop out. (I'm not saying this is a good thing, just that it seems to happen!)
Also, might be worth a word with his teacher. Our school has different days of the week that different years are allowed to play ball games, and no ball Fridays. I think it's partly a space issue, but partly to give the non ball-loving kids a bit of respite from football dominating the play. My son doesn't like it much, but I still think it's a good thing!
Trying other sports is a really good idea too - to help with confidence and also possibility of bonding with like-minded people. Non-footballing boys I know do surfing, parcour, tennis, hockey etc.
One more thought: if he is interested in football (even if not playing particularly) that can be very useful for playground conversation. If he does have some interest, might be worth encouraging him to support a team, take an interest etc to be able to talk about it at school. (Obviously if he isn't interested, I'm not suggesting he has to pretend to be to fit in!)