City still trail Manchester United by 12 points at the top of the Barclays Premier League even after winning at Old Trafford on Monday night.
With just seven games remaining only the most optimistic of City supporters would believe the deficit can be overturned and most are instead looking forward to Sunday's FA Cup semi-final against Chelsea.
Mancini said: "If United lose against Stoke and we win against Chelsea in the FA Cup and win against Wigan [in the league next Wednesday] - six points, it could be possible.
"But we need to have three points for the FA Cup!
"It is impossible. They did better than us, they deserve to win."
Mancini conceded defeat to United after a damaging loss at Everton last month and Monday's deserved 2-1 success has not changed his mind.
But the Italian feels the current gap is not a fair reflection of the difference between the sides and he is keen to reduce it to a more appropriate figure.
He said: "The championship is not important, it is finished, but it is important we showed we are like them.
"Twelve points is too much. We hope to get closer. We have seven games, so we hope."
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