And the feeling at City is that a win would be a giant stride towards starting to close the gap on their cross-town rivals.
The City boss says he will not shy away from fielding the attacking front four which has unhinged opposition defences in the Blues' last three games.
But he added that he wants to weigh up what midfield resources are available to him before finalising his team, with Wayne Bridge, Patrick Vieira, Pablo Zabaleta and Stevie Ireland all likely to be available after injury.
"I want to see who recovers," said Mancini. "It is important when you play with two wingers and two strikers that you get the balance right. If the winger works for the team, it is better to play like this.
Respect
"But if not, it would be difficult."
Mancini says that there is still plenty of hard work to be done before City can look United in the eye as rivals for the top honours.
He feels the gap is closing steadily, but one area where the Reds still have an edge is the strength of mentality required to remain at the top, something which only comes with success and experience.
"United have a good personality because they have won a lot of titles in the past," he said. "They have strong players and a fantastic manager, and that is why we have such respect for them.
"It's important we play 100 per cent and concentrate for the entire game. We also have to improve if we want to get to their level. That means a lot of hard work, but we can do it."
Tomorrow will be the first staging post on that journey, and Mancini has kept his cards close to his chest this week.
But he has not been afraid to play with two wingers and two strikers, despite accusations of negativity from some quarters.
City's wide men Craig Bellamy and Adam Johnson both work back for the team, so Mancini would be happy to keep them ranging down the flanks, with Carlos Tevez and Emmanuel Adebayor providing a threat down the middle.
This is new territory for the Italian. He has played three matches against the Premier League's top two United and Chelsea since taking the reins at the Blues in December.
In all three, he plumped for a three-man triangle in midfield, with two wide men and Tevez alone up front.
But Adebayor was not available for any of those games, and that puts a new slant on things. Since he has returned, Mancini has consistently picked two front men, and has been prepared to weaken his midfield to do so.
His dilemma this week has been whether to stiffen his midfield or not - he would probably have to drop either Adam Johnson or Adebayor to the bench to accommodate such a tactic.
Space
He and Bellamy could be key players for City. United often favour a five-man midfield, with Nani and Antonio Valencia breaking forward - and they need to win the match, which could leave space for the Blues wide men to go at the full backs.
Mancini has to decide whether to try to negate the Reds' midfield or exploit the fact that they will be on the front foot.
Another interesting note is that the only player to have played in every game under Mancini, until missed the last two games through suspension, was Zabaleta.
If the manager wants to accommodate the adaptable Argentine, he could stick him a three-man midfield or replace Nedum Onuoha at right back, which would be somewhat unfair on the big Mancunian.
Bridge, meanwhile has recovered from a hernia operation, which caused him to miss five matches.
The derby kicks off a run of tough games but Mancini is relishing the big matches, believing his players respond better to the challenge.
"The last five games are hard games, and massive games, and this is an important month - but I like it that way," the City boss added.
"I am confident we can beat United, because we have improved a lot in the last month. We will go out to win, as we always do."
What formation should City play? Have your say.
Tweet
mcfc_daz (16/04/2010 at 10:12)