We have to either have a Club Developed Player in the matchday squad or in the registered 22-man Squad List if we want the full allocation of 7 subs.
Our qualifying players for that role are Cody Johnson, Ashton Mee and Ethan Pye, who all happen to also count as U21 players so don't need to be registered in the Squad List to be available to play.
We could, in theory, not register any of the 3 and still have 7 subs but if we couldn't name any of them in a matchday squad for whatever reason then we'd only be able to have 6 subs for that game.
Realistically though, we'll probably name 1 of them in the 22-man Squad List like we did last year with Cody Johnson; I'd imagine that player would be Ethan Pye given his likelihood to play regularly.
If that's the case, Cody Johnson can go out on loan without any impact.