For the first time in his managerial career at Old Trafford, Sir Alex Ferguson will head to Tottenham Hotspur on Sunday to face a home side who are genuine title contenders.
Spurs are in fourth spot, just eight points behind Ferguson's side but the North Londoners have never had to combine a Premier League challenge with a simultaneous assault on the UEFA Champions League, and that will be their biggest test yet, says the United boss.
"The big test for Tottenham will be whether they can combine all the different fixtures they have when the Champions League starts up again in February," Ferguson said. "If they're still figuring in the Champions League in March, then combining that with the Premier League and FA Cup will be the big test for this Tottenham team.
"I think this is the first time, certainly in my time at United, where we have gone to White Hart Lane with Spurs challenging for the championship. That is measure of their change in fortune under Harry. He has done a fantastic job there and Spurs have some really exciting players there now.
"Obviously the development of Spurs is an interesting one because I can't remember ever taking United to the Lane with Tottenham challenging for the league. I don't think I have ever done that."
United are expected to have Wayne Rooney, captain Nemanja Vidic and Edwin van der Sar in contention after the trio all missed last weekend's FA Cup win over Liverpool. One man who did feature in that encounter was evergreen winger Ryan Giggs who is expected to make his 600th league appearance for United in the London encounter.
"He is just an incredible human being and he defies the logic of being a forward playing the way he did last Sunday," Ferguson said. "We know how to manage him now and he doesn't play every week but when he does he makes a contribution that lifts the team.
"I thought he was outstanding last week and he has that capability and fitness. He ran for 90 minutes up and down the pitch and he has been doing that for two decades. There is no other player who has done that or who is ever likely to do that. He is an amazing man."