All eyes will be on Cristiano Ronaldo when he faces his former club this week, but a face from the past has popped up to indicate he could also have his say.
That man? Ricardo Izecson dos Santos Leite, who we all know simply as Kaka.
Kaka has not enjoyed a good time of it since signing for Real Madrid for £56 million back in 2009. Not only was his record transfer fee eclipsed within weeks by Cristiano Ronaldo, but CR7 has outshone him comprehensively on the pitch too.
Injuries have played their part too, but this season Kaka has certainly been lacking the spark of old, and is second fiddle to Mesut Ozil, once a United target.
The Brazilian came close to being loaned to former club AC Milan in January, with the player said to have pushed for a move, but the Rossoneri's priorities lay with Mario Balotelli.
It was with Milan that Kaka enjoyed the finest spell of his career, winning the Ballon d'Or, and earning that £56 million move to Madrid.
In 2007 he orchestrated the demise of Manchester United in the Champions League semi-final, scoring twice at Old Trafford, two away goals which would tip the tie in Milan's favour, before opening the scoring in a 3-0 win at the San Siro.
If he was to hit top form he is certainly a problem United would prefer to do without, and at the weekend there was a glimpse of the old Kaka sparkle.
He was handed only his second La Liga start of the season against Sevilla, his first in four months, as Mourinho rotated his side ahead of the big clash, and Kaka did not disappoint.
The Brazilian did not score, but he was full of life and a threat throughout, with Spanish newspaper Marca declaring: "For one day at least, it can be said the old Kaka was back."
Now it's simply an issue of what happens next, and while the playmaker is unlikely to start against United on Wednesday - It will be Mesut Ozil instead - Kaka has thrown his name into the hat to feature off the bench.
If Madrid are searching for a goal, or hoping to turn the screw on United, a player like Kaka has the experience to help them do so.
It will be a big night on the big stage, where the big players come to play. Who knows, it could even be the redemption of Kaka - And that is probably not an event United will have bargained for a couple of weeks ago.
What do you think? Could Kaka play a role over the two legs?
image: © Jan Solo