I think to have a player get over 80 minutes by having him play 2 games he must indeed be a lot better then the back-up, and have decent stamina.
the question is, does he field back-ups at all, or just has his 1 player play the whole game? ...
In (almost) any 'normal' situation every team is capable of fielding the same player as starter twice and suffer no ill effects on form. Give a back-up is lined-up, and the player isn't put into a third game as starter nor back-up nor reserve.
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