Off the pitch, it would be fair to say there is a mutual respect and admiration between the two, borne out of their career accomplishments and a history of fierce duels in the past.
If Real lose to the Red Devils, though, it may signal an end to the Portuguese coach's time in Madrid.
This article will consider this and other potential ramifications for the two-leg tie, looking at how a win or a loss might affect each club.
The bottle of wine getting uncorked? That's just a given.
A Real Madrid win is perhaps the result predicted most by neutral fans and pundits alike.
Jose Mourinho has the edge over Sir Alex Ferguson in terms of past results, while the Spanish side also possesses the best player of the two.
If all goes to plan for Los Blancos, Mourinho will feel massively vindicated in the face of those who have called for his head in the past few months.
Champions League glory is the number one priority for most in Madrid, and with a win over the Red Devils under their belt, they would have all the confidence they need to go deep in this season's competition.
If this were to be the case, Real's poor domestic standing could be somewhat overlooked, while the men of importance might feel the need to make fewer changes in personnel come the summer.
With the club pushing for glory on the biggest stage, Cristiano Ronaldo may be able to sleep a little easier at night—his apparent unhappiness reduced to a mere discomfort.
If the Portuguese superstar were to put in a couple of match-winning displays, a few more people may be more willing to put him at the same level as Barcelona's Lionel Messi.
A win would also restore a lot of the fans' faith that has been lost this term, or at the very least temporarily quieten the naysayers.
If Manchester United can claim victory over the two-leg tie with Real Madrid, a lot of people will be proven wrong, while fans of the club will feel a sense of vindication.
The standard of the current Premier League has been slated by a good number of people across the continent, but if the runners up of Britain's top league can beat the reigning Spanish champions, such voices will be hushed.
After dodgy performances against the likes of Tottenham and Norwich this season, many declared the club in a state of crisis. But now, the Red Devils seem to be peaking at exactly the right time, as they often do.
If Robin van Persie plays a major role in a win, much of the post-match reaction will be centred on him, some of it criticism aimed once again at Arsenal for selling a true difference-maker to one of their rivals.
But in truth, United are far from being a one-man club. Perhaps a convincing victory in the Champions League will awaken people to this fact.
The legend of Sir Alex will build, while the budding careers of youngsters like Phil Jones and Rafael would jump forward a notch thanks to the experience.
In the long term, a high profile win would also make Old Trafford more of a desirable destination for potential transfer targets.
The aura surrounding the club that has dimmed a little since Ronaldo's departure would make a glowing comeback.
There is one very real possibility should Real lose to United—that this will be Jose Mourinho's last season at the club.
There is clearly enough talent in the squad to beat the Red Devils, so the blame for a loss would most heavily fall on the Portuguese coach's shoulders.
With a premature exit from the Champions League and the La Liga title all but won by Barcelona, fans in Madrid would be facing a very barren few months before the summer.
There is always the Copa del Rey, but for a side that many expected so much from to only be fighting for a lesser trophy at this stage of the season, this would be unacceptable.
A loss might also push Cristiano Ronaldo further towards the door, even if it is unlikely that he leaves Real this year.
The club's fans would naturally grow more disenchanted, and cries for a landmark signing to be made at the next possible opportunity would grow in number.
A sense of gloom would hover over the Bernabeu for a long time to come—or at least until the end of the season.
Despite their excellent league position, should Manchester United lose to Real Madrid, major questions will be asked of Sir Alex and his team.
It has been awhile since the Red Devils convincingly beat a top side from the continent—not since before Cristiano Ronaldo moved to Spain have United been considered a major contender to win the trophy with the big ears.
The draw for the Round of 16 was certainly unkind to the side, but Real is the type of team that must be beaten anyway on the road to victory.
If there is one major regret that Ferguson would have were he to retire today, it's that teams of his weren't more successful in the Champions League.
A promising campaign will be stopped dead, with serious doubts raised as to whether or not this current squad will ever be good enough to go all the way.
One very minor positive from a potential loss though would be the ability for United to focus more on wrapping up the Premier League title and claiming FA Cup glory.
It is because of this that Manchester City boss Roberto Mancini will be hoping his domestic rivals can come away with a landmark win this Wednesday.
What might the aftermath of a Real or United win be like? Will Jose Mourinho be fired should Los Blancos lose?