Chance he'll start against Lyon tonight because of injuries to Gundogan, Bernardo and De Bruyne. It's more likely that Pep will play Sane and Mahrez with Sterling next to Silva, but who knows?
As for his potential in later years, I find it curious to see so many United fans suddenly very protective over, and concerned about the playtime of, a City youngster. He's 18. If he's still not starting games in double figures over the course of a season by the time he's 20/21 then I'd understand him wanting to explore other options, but for now he needs to be managed carefully whilst earning his place in the side. Twenty minutes here in the league, ten minutes there in the Champions League, a start in the FA Cup 3rd round, that sort of thing.
Some youth players don't suit that kind of approach. We've seen over the years with players like Rooney and Lukaku that some young lads suit making 40+ appearances a season in their teenage years. It sometimes means they burn out by the time they're 30 (or even earlier) but it that just means their best years were between the ages of 17 and 28 as opposed to 22 and 33. Every human being is made up of different ingredients. At the moment Foden doesn't have the physical stature to compete as often as his technical ability suggests, but he's getting there.
And that's all he can do: slowly get there. He might get more game time out on loan at another club, but what he needs right now is coaching. The following is a quote from Ross Barkley:
"Over the years I haven't really been coached much. When you go through the youth system, you're always going in to do analysis work, you're looking at every way of improving and your coaches are always on top of you. And once you go into the first team it can change, because game to game managers are focusing on weekly results, not player development."
Would we want Phil Foden to be saying the same thing in five years, having failed to really make his impact in the way Barkley hasn't quite managed to live up to his potential? No. You want him protected, you want him eased in to the reality of being a professional footballer for one of the best teams in the world. Players like Sancho are lucky because he's managed to get a spot starting for Lucien Favre but Foden could end up playing for a terrible coach. Barkley was one of Everton's key players but if he wasn't being coached then he was never going to progress.
So I'm not going to lose sleep over Foden not playing 90 minutes for the while.