If a player "Needs a rest" I never tell them I am resting them and drop them for the next game, in my experience that is asking for trouble.
I just send them on holiday for a week, if they need to be fit for the next game I rest them from training for the time in between the games, that is a short term fix that works for me without upsetting the poor darlings.
I don't mean to be critical, but as NineCloudNine says, the problem requires better management.