Manchester United manager Sir Alex Ferguson believes Manchester City have replaced Liverpool as the club's biggest rivals.
United and Liverpool are the two most successful teams in England with 119 honours between them.
But Ferguson now considers City as a greater enemy after they clinched the English Premier League title last season.
"There is no question that over the last quarter of a century Liverpool-United games were unbelievable and always the most important games," he said.
"But it has shifted in the sense that at this moment Liverpool are not challenging for the league the way that City are.
"They are our biggest threat and we are their biggest threat now so that has changed.
"That is the great thing about football, things can change."
City, second on the table, host leaders United at the Etihad Stadium in what shapes as the biggest game of the season yet on Sunday.
"There is such a long time to go until the end of the season," Ferguson said
"We have won leagues when 12 points behind and lost a league from 11 points ahead of Arsenal until we got a deluge of injuries, so you can never be sure and you can lose to anyone.
"We have lost to Norwich already this season but that is the kind of league we are in and it is a tough league.
"It is going to be close between the two sides, there is already a big gap over Chelsea and Arsenal and Tottenham.
"There is a gap and I think it will be difficult to imagine both of us would collapse and allow another team in so I think it will be between two of us."