Ferguson said: "Gerrard is a fabulous player. I think Roy and him are different types of player, but in terms of the influence on their team, they are both the key men.
"I rested Roy for three games before we played Rangers which was to make sure he was fresh to play Liverpool. He's still such an important player for us.
"I am really looking forward to this match. The Manchester derby is a great occasion but nothing beats Manchester United v Liverpool. This is the big game of the season.