It is the job of these two coaches to provide a sound game plan for their players and ultimately put them in a position where they can succeed.
With United—away at the Bernabeu—underdogs in the first leg, Sir Alex brought a conservative approach to the match. As shown by Zonal Marking, United played in a standard four-defender formation but further supplemented their defense by placing Phil Jones and Michael Carrick in defensive midfield roles. As United sat back and let Madrid attack, the Spanish side garnered a whopping 61 percent of possession, all the while putting 28 attempts on United's goal.
In the second leg, that needs to change.
With their fans behind them at their home turf, United should be looking to play the attacking-style football that Old Trafford has been witness to for years. This means possibly implementing a more attacking-minded formation to get at the Madrid goal, such as 4-3-3 or 3-4-3.
Sir Alex is not one known to experiment with formations, however (he just changed from a 4-4-2 this year), so a more realistic move would be allowing the defensive midfielders to roam more into Madrid's half.
The inexperience of Madrid's defense is another reason Sir Alex should demand attacking football from his players. Real Madrid will once again have backup keeper Diego Lopez in net, who has a mere one clean sheet in 11 La Liga appearances.
In addition, Mourinho made a questionable move by starting 19-year-old Raphael Varane at right center-back in the first leg. If he opts to do so again, Sir Alex should start a true wing player—like Nani or Ashley Young—to terrorize him with pace and footwork throughout the match.
Even if United do implement an attacking formation, they still need defensive presence, something Shinji Kagawa will never give them. In the first leg, the flimsy Japanese midfielder was never really involved, as Madrid's midfielders—Sami Khedira and Xabi Alonso—constantly bodied him off the ball and infiltrated the United half with ease.
Better options for Sir Alex would be Anderson, Tom Cleverley or even Paul Scholes, a purely physical midfielder who can surely clog up the middle, even at 38 years of age.
While Khedira and Alonso are talented players who need to be contained, Cristiano Ronaldo is truly on another level. The Portuguese attacker has an otherworldly 183 goals in 181 appearances for Los Blancos and is obviously the focal point of their attack.
After a truly dominating performance by Ronaldo, Sir Alex will be thinking of ways to slow him down, which won't be easy with agile midfielder Phil Jones likely out for the second leg, per The Sun:
United's best bet to contain Ronaldo lies in one of their own stars: Wayne Rooney. Whether or not Sir Alex will want Rooney in this kind of role will remain to be seen, but the Englishman is truly the man for the job. Known for his gritty style of play, he is probably just as strong as United's defenders and possesses the speed and agility that many of them don't.
Simply put, Rooney, unlike others, is not afraid of Ronaldo and has no reason to be with his physical attributes.
Lastly, Sir Alex needs to utilize Javier Hernandez off the bench. With his uncanny eye for goal (he's got eight in five EPL starts this year), the Mexican forward deserves a chance to prove his worth once again. Plus, he is somewhat of an unknown commodity to Madrid, having sat out the first match. This could confuse Mourinho's defense and maybe even allow him to produce the magic he has come to be known for.
Ultimately, United will need to be on their best form to beat an extremely talented Real Madrid side.
And that all starts with Sir Alex.
(All stats and info via ESPN FC)