If Real Madrid is to have any hope of doing the improbable, it will need Cristiano Ronaldo fully fit and ready to run.
The winger picked up a thigh injury in the 4-1 first-leg defeat against Borussia Dortmund. He sat out Madrid's 2-1 win over the weekend against La Liga rivals Atletico Madrid. Fortunately for the club, he's been declared fit for the second leg on Tuesday (h/t Reuters via The Independent).
However, being declared fit and actually being fit are two different things. If he's on the pitch, Ronaldo needs to be 100 percent.
Lionel Messi was determined to be fit for Barcelona's clash against Bayern Munich. Unfortunately for Barca, Messi looked off the pace. He didn't truly look fit at all and contributed little to the match.
Scoring three goals without reply is a tall order for Madrid even in the Bernabeu. Dortmund is a strong side. Plus, with the lead, the Germans will look to sit back and make Real Madrid come right at them.
Ronaldo is either the best or second-best player in the world, depending on whom you ask. Madrid is a much worse club when he's not on the pitch. Any club would be. All the talent in the world can't make up for missing a transcendent player like Ronaldo. Look at how much Barca has struggled when Messi isn't out there.
It's matches like these in which your star players need to step up and have fantastic performances. Madrid and Dortmund are full of the top players in the world at their respective positions.
Ronaldo is in a different stratosphere, though. On almost every occasion, he is a cut above any of the other 21 players on the pitch. Ronaldo isn't just world class—he's legendary. When he's on his game, no team has an answer for him since he is that much better.
If Ronaldo is only 70 or 80 percent fit, though, he becomes just another very good player in a match already full of them.
The winger is also a crucial part of Madrid's tactics.
Real Madrid's success has centered on its lethal counterattack. There isn't a club any better than Los Blancos at hitting back on the break. A lot of that success has been predicated on having a quick player like Ronaldo out on the wing.
Think back to how Madrid scored its only goal in the first leg. It was off a throw-in. Mats Hummels made a mistake, which Gonzalo Higuain pounced on. Then it was Ronaldo there for the easy finish. The goal came out of nothing and was born out of the speed of Madrid's counter.
Dortmund did a great job of limiting Madrid's counter opportunities and will do the same on Tuesday. That's why Ronaldo will be so vital. He needs to help Los Blancos make the most of what few opportunities the club has on the break.