The Italian was the target of criticism after defeat to the Eredivisie title holders left them with little hope of qualifying for the knockout stages of the competition.
When asked if he had endured a difficult couple of days, Mancini responded to reporters: "For you or for me?"
Speaking ahead of Saturday's fixture against Swansea City, Mancini added: "If you are a top player, it's not important which system you use. If you don't understand, you can't play for a top team."
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He continued: "I don't want to speak about Micah because I don't think he said this. He answered questions. It's not important. I understand you should write about this, but for me it's not important what Micah said after the game.
"With this system, every time we change the result. Maybe Micah doesn't know this because it is the first game for him after he was out for two months. Probably he has worked less than the other players but maybe the next time when we play this system, he will understand it better." The Manchester City boss remains confident that his side are able to get results by playing just three at the back, and insists that this is not just something which he started experimenting with this season.
He added: "The players know the system. When you are on the bench and 2-1 away, the manager should do something from the bench. We wanted to play more offensively and we conceded a third because of a mistake.
"I repeat, this system we played a minimum of 15 times last year. It is not a new system."