The Manchester City boss selected Mario Balotelli, Carlos Tevez and Edin Dzeko for the recent encounters with Aris and Fulham.
Although the policy worked against Aris as City cruised into the Europa League last 16, it did not in the Fulham encounter when Tevez and Dzeko failed to impress.
"At this moment I don't think we can play all three," said Mancini. "The team is too tired.
"Maybe when all the players have recovered and we have more options but as it presently stands, it is important we have proper balance."