Alex Ferguson has claimed it would be one of Manchester United's best ever results if they were to beat Manchester City on Sunday.
Although United head to the Etihad Stadium three points clear of their neighbours, who were dumped out of Europe altogether on Tuesday, Ferguson is adopting a cautious approach.
In his programme notes ahead of last night's 1-0 defeat to CFR Cluj, Ferguson outlined his belief that both sides may opt to play safe.
The United boss is particularly fearful of his leaky defence.
And it leads him to conclude it would be a significant moment in his Old Trafford tenure if the Red Devils were to come out on top."
If we win [on Sunday] it will be one of our best ever results," Ferguson told MUTV.
"They are a really good, powerful team with massive players.
"It won't be easy and if we defend like we did at Reading we'll be in trouble.
"The important thing for us is to take lessons from the mistakes we're making and do something about it. We need to find a solution."
"If we defend like we did at Reading we'll be in trouble" - Alex Ferguson
With Chelsea and Arsenal sliding out of the picture, and Liverpool having never been in it, even at this early stage, it appears to be a straight battle between the two Manchester clubs this season.
Ferguson, who has a fitness doubt over Tom Cleverley, is not buying into that assessment.
"At this time in the season you can't really say it's a two-horse race," he said.
"If you think back we were 12 points behind Chelsea at one point and when Arsenal beat us in the league in 1998 we were 11 points clear."