Player of the field for treatment.........who is covering?

I'm starting to get really frustrated!!! every time a defender gets a knock and has to leave the field for treatment, it leaves a GAPING whole in my defence. this is particularly annoying because none of the midfields drop in or the defence doesn't narrow to cover this so i'm often left with a striker free.

on numerous occasions the opposition strikers have scored goals against me because they are unmarked.

by the time i'm allowed to make an adjustment, the player is back on the field so there isn't really much i can do except concede goals.

hopefully this can be fixed in future version but has anyone else been punished by this lack of intelligence?