Manchester City go into the clash as Premier League leaders, but they are only two points ahead of United - meaning that a win for the Red Devils would hand them the top spot.
When asked if it is the biggest Manchester derby since he took over United 25 years ago, Ferguson said: "Yes, I think so.
"The last couple of years it's become more intense and a lot more importance has been attached to the games.
"With them top and us second, it builds up to a fantastic prospect for everyone. I'm looking forward to it."