Manchester United boss Sir Alex Ferguson admits Monday is the biggest derby in their history.
For the red and blue fans, victory will define "the most important day of their lives."
Ferguson said: "It means everything to the supporters. Going in to work next Tuesday morning will be the most important day of their lives - for both sets of supporters.
"It's there. People have inherited this from grandfathers and great-grandfathers. And grandmothers. You cannot change a family's traits. That's what supporters are.
"There was one banner recently at Rangers that said 'I've been supporting Rangers for 139 years.' I thought 'He's done well!' Did you see that? That sums it up.
"It's in the blood of these supporters and I know lots of supporters who would give everything to win this game on Monday."