Sir Alex Ferguson has claimed Manchester City "might have fallen apart" this season had it not been for the fact they had the Barclays Premier League title in sight.
Both Manchester clubs head into the final game knowing they could end up as champions.
However, City have the clear edge thanks to their goal difference advantage, which means if they beat QPR at the Etihad Stadium it would secure them their first title since 1968.
It represents a major achievement for manager Roberto Mancini, who has had to deal with numerous issues, including Carlos Tevez's lengthy absence from the club and Mario Balotelli's erratic behaviour.
"It is obvious all the things he has had to deal with," said Ferguson. "If he didn't have the closeness to win the league, it might have fallen apart."
Instead, City look set to be crowned champions, setting United a challenge Ferguson likens to the one Jose Mourinho laid down following his arrival at Chelsea in 2004.
"We had to contend with Jose's management style, which was very effective," said Ferguson.
"He did a fantastic job there.
"You knew you were competing against a very clever manager. You weren't just facing the money, you were facing a very united squad.
"They were hard to beat. City - quality-wise - are very similar to Chelsea at that time.
"Some of their players have had outstanding seasons. When you win the league you need five or six players who are consistently good all the time.
"City have had that this year and the manager, for most of the part, has done well."
However, even if City do not make the "stupid" mistake Ferguson says it requires for his team to land a 20th crown, he will not back down from the challenge.
"We have to do something about it," he said. "That is the only thing we can do.
"We have to meet challenges and the good thing is that we tend to get there in the end.
"In the situation we are in at the moment, it looks as though we are going to lose out this season.
"But there are a lot of young players in the squad. We don't look, in any way, as though it is the end of a period for us.
"In many ways it is the start for a lot of young players here. The challenge is very obvious to them now if we lose the league.
"As we did when Chelsea won the league two years in a row, we have to do something about it. We managed to do that. Hopefully we can do it again."