Sir Alex is also quick to recognise that the derby has now become the most important fixture on United's calendar.
"Liverpool and United games over the last 25 years have been unbelievable," he said. "They've always been important games. But it's shifted because, at this moment, Liverpool aren't challenging for the league like City are.
"City are our biggest threat, so that's changed. And we're their biggest threat. We have to accept their challenge like we did when Chelsea came along and when Arsenal overtook Liverpool in the early 90s. We have to do it again."