The Argentine is eagerly anticipating Tuesday's encounter and has underlined the importance of the match calling it "the biggest game of the year" for Jose Mourinho's men
The Spanish champions were held to a 1-1 draw at the Santiago Bernabeu in the first leg of the round of 16 tie, and Valdano is eagerly anticipating the return.
"After the match at Camp Nou, Real Madrid are brimming with confidence ahead of the biggest game of the year, which comes at Old Trafford against Manchester United," Valdano told Cadena Ser.
"Nothing matters more than winning the Champions League, the club's 10th European Cup.
"The match at Old Trafford will be much more tactical than the Barcelona game.
"Against Real Madrid, the home fans will be understanding if [Sir Alex] Ferguson decides to set up his team to play conservatively, and I think that will be the case."
Madrid will host Barcelona on Saturday in La Liga before Tuesday's match at Old Trafford.