United can open up an eight-point lead over Manchester City with wins over Blackburn tonight and QPR on Sunday, before City next play.
Mancini, whose City side dropped points at home for the first time in 15 months in their 3-3 draw with Sunderland, said such a margin would be too big to close.
“If we go eight points behind then it is finished,” said Mancini. “It’s clear we are disappointed. We have made some mistakes, me and the team.
“We have also been unlucky, like losing three or four key players at an important moment. But when you are a strong team you should be able to pass these difficult moments. Yet football can change in two or three games.
Can you imagine Fergie or Mourinho or Guardiola waving the white flag with some many games to go in the season?
And how will City’s players react next weekend when they face Arsenal if United have beaten Blackburn and QPR? Will they just go through the motions knowing that their manager has surrendered to their biggest rivals?