There no cheap answer to that problem...Its simply be prepared play a weaker team for the 2nd or later match...Or get the tokens out to buy booster packs...

One thing i have noticed though is that players will still perform to somewhere near there best at around 85% peak fitness. Si there's no need to have all your players 100% for all the matches...Especially against lower rated teams

I am on level 6 and have won or finished second every league season so far with 2 C/L wins to boot. I just try to organise my self to allow a good mix of quality and fitness between my squad to allow for two matches a day...