Mancini believes his best team can match United's, but he acknowledges Ferguson's camp have a depth of talent, experience and organisation that sets them apart.
The Italian said: "United is a strong team, but the difference is in the 20 players, not the 11.
"Probably if we played our best 11 players against United's best 11 players they would not be better. But we are not ready to lose three or four players.
"Maybe next year if we have more players with strong mentality it will be enough.
"United are better as a club and in their mentality. That is because they are used to staying on top. They can play without problems.
"They maybe don't have the pressure we have because they have won everything. When you play a team like United, that is the difference, not the players."