City go into Sunday’s clash two points clear of the current champions, a situation the Red Devils have not been used to in recent years, and the United boss is more than aware of the importance winning.
“This game could be significant at the end of the season," said Sir Alex. "It is a six-pointer. It will make a difference to whichever team wins it.
"But it is early doors and you can recover," he continued. "There is no doubt about that. With our record in the second half of the season, you hope that we will be better."
Roberto Mancini’s men are the latest side to challenge United, who have dominated the Premier League for two decades, seeing off the likes of Chelsea, Liverpool and Arsenal.
And while the United boss is aware of City’s current form - having only dropped two points this season - he believes his team have what it takes to deal with their new challenge, with first choice defenders Nemanja Vidic and Rio Ferdinand now available for Sunday’s derby.
"We always accept a challenge at this club," he added. "We have had that time and time again. This is another situation. It is another game in the history of our club and we have to do something about it.
''They are top of the league. We have to do something about it," Sir Alex continued.
"You don't always want to be behind clubs, like we were for a couple of years with Chelsea. But we showed we had the vigour and determination, and also the decision-making that got us back in front of that particular football club."
A City win would be only their second success at Old Trafford in 37 years, but the United boss is relishing the task ahead, adding: "It is an exciting prospect.
"City have done fantastically well and if they had not thrown a two-goal lead away at Fulham they would have been top of the league with a 100 per cent record."
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