Keown wrote in the Daily Mail: "At 19 years old, he must be the best young central defender in Europe and I understand why Real Madrid paid close to £9million for him at the beginning of last season.
"They sent Zinedine Zidane in a private jet to make sure they signed him from Lens ahead of Manchester United and it was a good decision.
"Pepe was left on the bench for Varane in the first leg so it is now a big call for Mourinho whether to repeat that selection.
"The way Varane reads the game is exceptional. He is rarely beaten to the ball, not just because of his pace but because his positioning is so good."