Real Madrid against Manchester United is a match-up worthy of a Champions League final. It's going to be an open game and it will be the teams' form on the night that will settle the debate.
Both sides have the talent to make a difference and it's very difficult to predict a winner.
Of course, the big story is Cristiano Ronaldo playing against his former club. The Portuguese is a great player who is one of those who can settle any match, but because of the back story and his time in Manchester, his performance will certainly be under the microscope.
With Madrid no longer in the running for the Spanish title, they have fewer obligations than United to get domestic results. You could say that Real Madrid's entire season rests on this one tie, but that also allows Jose Mourinho to rest players between the two legs.
I'm not sure if Alex Ferguson will leave United in the hands of Mourinho, as rumours have suggested.
I don't think it will be Ferguson who will decide who replaces him. We can perhaps ask his opinion, but it is not necessarily his job to think about that.
It's possible that he would like Mourinho to succeed him, but I think that will be the furthest thing on both managers' minds when they get to kick-off on Wednesday.
A quick word on my fellow Frenchman Raphael Varane, the 19-year-old Real Madrid defender who could face United: I'm happy for him because he's carving out a role at one of the world's best clubs, which is remarkable.
Yet at the same time, when you are in charge of a club like Arsenal, you have to wonder why this player is not playing for us. He was at Lens, and we might well have caught him there.
It was a risk for Real Madrid to sign him at his age, but when you have such a talent, you can overcome everything.
He has benefited from suspension to Sergio Ramos and injury to Pepe, but nevertheless Mourinho has chosen him to step in.
His next challenge is to manage the increased media exposure on him, especially now he is in the French national side.