City must secure second spot and lift the FA Cup to give Mancini the semblance of further progress after last year's momentous exploits.
"It is impossible United can lose 15 points in eight games," said Mancini.
"Even if we win at Old Trafford it won't change anything. The league is a fight for second. We can say nothing about first place.
"All we can do now is our best in the last eight games and also in the semi-final."