I feel you for the form thing, I understand how it is when GS forces you to not field a player. Well I definitely don't know what you're facing, but I've always found the best way to solve this is to talk things out with the managers.
Iirc NT players who don't play that week don't get their merchandise boost, which is something you can educate the managers on (and its gonna have a bigger impact compared to the U21, coz iirc NT merchandise boost is directly proportional to salary).
No worries, there's a whole season ahead of you. Good luck mate!