The two heavyweight title rivals meet at the Etihad Stadium in one of the biggest and most eagerly-anticipated matches in Barclays Premier League history. With City trailing league leaders United by just three points going into the game, the stakes are high, but Mancini has continually played down his side's chances.
The Italian said: "It is impossible to be worried for Monday yet. It is football, not work. Maybe Monday morning there will be pressure, but this is normal for us or for United. But not now, I don't think this."
Even though victory would take City back to the top of the table, Mancini insists United would remain title favourites and because of that, he says the pressure is yet to show.
Mancini first wrote off his side's title prospects after a damaging defeat at Arsenal three weeks ago left them trailing by eight points. He has maintained that stance despite City cutting the gap with impressive successive wins over West Brom, Norwich and Wolves, while United have faltered against Wigan and Everton.
With a testing trip to Newcastle and a home clash with struggling QPR still to come, Mancini says his side have the harder run-in as United play Swansea and Sunderland.
Mancini said: "Now we have this small chance but I think it is important that after Arsenal we just continue to play football. We have only one chance because they lost a point against Everton, but I think it will be difficult.
"They have one difficult game against us, then they have two easy games. They will probably get six points. It is clear if we have a chance - we want to take that chance - but I don't know."
City have not won a league title since 1968 and for a club that was in the third tier 13 years ago - while United were winning the Champions League - Mancini feels considerable progress has been made.
He said: "For us, I repeat, we should be proud for our season. We have 22 points more than Chelsea, who went to the final of the Champions League. We have 14 points more than Arsenal, 31 more than Liverpool and they are another top team. We should be pleased for this."
Source: PA
Source: PA