If someone was to leave from the midfield, it's not Tchouaméni, only one season, has shown glimpses of quality, and hasn't been amortized for FPF.
I doubt any young midfielder is leaving, as this is probably Kroos and Modric's last season and their participation should be as rotation players, not starters, they don't have the legs to play 90 minutes, specially together.
If someone would leave( as I said, not needed even if Madrid bought Mbappé) I would think it would be Valverde, he´s been poor for a while like the rest of the team, was a cheap signing, is amortized for FPF and you would still get a fat check seeing premier league paying 100M for nearly anyone.