Real travel to United for the second-leg of their Champions League last-16 clash and Ronaldo returns to familiar grounds since his record breaking move to Real in 2009. Former England captain Beckham feels the atmosphere at Old Trafford will inspire the Portuguese.
"Many things inspire great players and him going back will be a special night for him, Neckham said. "The fans love him and it will be a great occasion.'"
"When you go back, you enjoy the occasion, of course, and I am sure it will inspire Cristiano," said Beckham, who scored 85 goals in 394 appearances for United between 1992 and 2002.
Real Madrid dominated the first-leg but United held on to a much needed 1-1 draw at the Bernabeu. Ronaldo equalised for the Spanish champions after Danny Welbeck put the visitors ahead.
Beckham was confident Ronaldo will impress against United but was not sure who are the favourites in this clash.
"It will be a great game to watch. It is hard to say who will win. Two great teams with great players," he said.