The two Manchester clubs go head to head at the Etihad Stadium with the Citizens trailing the Red Devils by three points.
With a superior goal difference, victory for Mancini's charges will put them back in pole position for the Premier League title.
However, the Italian has said that their local rivals have an "internal force" which has bred much success over the years.
"For the last 20 years Manchester United have been winning constantly," said Mancini. "Even when they are coming from behind in the table, they know deep inside they can come back. They have this internal force born from all the success they have had.
"Playing often against United has helped our progress and allowed us to learn. We've moved closer to them but they are still better than us. They have more experience and that team spirit that we are in the process of building here.
"We are always behind United and we are obliged to win on Monday, as United still have a big advantage and an easier run-in. The match against United could end up not deciding anything."
Man City are bidding for their first title since 1968.