Mancini has already admitted City need "a miracle" to salvage their Group D campaign after taking just one point from their opening three games. The Italian reiterated after Saturday's bore draw at West Ham that the Barclays Premier League champions were "not ready" to be crowned kings of Europe.
But he insisted he would not tolerate them crashing out of the Champions League with a whimper for a second successive season. "You should play 100 per cent every game. It's normal, no?" he said. "We have three games. We have to think only about Ajax at this moment and we will see what happens."
Asked if his side owed him a big performance on Tuesday, Mancini replied: "I think three big performances!"
Indeed, the City boss revealed he would demand three improbable victories from his side against Ajax, Real Madrid and Borussia Dortmund, which would see them complete a remarkable comeback to qualify.
But he added: "I don't think that we are ready to win the Champions League. If we say this, we are not honest. We are a good team. We are not ready like the other teams."
Mancini bristled when it was pointed out Chelsea won the Champions League last season despite finishing sixth in the Premier League, 25 points adrift of City.
"But Chelsea for how many years tried to win the Champions League?" he said.
"Chelsea were probably the best team in Europe for 10 years and they won the Champions League after 10 years, probably when they didn't deserve it.
"Probably, they deserved to win the Champions League three or four years before. If we are very good, we are fantastic, we win the next three games, everything can happen. But, before, the way is very long."