In-form England forward Rooney, who scored twice in United's 3-2 first leg win, is a doubt for the Champions League last-16 return match due to a knee problem.
"I'm sure Rooney will play. I think he's had some problems in the last few days but he had the whole weekend to recover," former United player Beckham told Milan's TV channel on Monday.
"He's a fine player and he'll want to participate in the match. Alex Ferguson will certainly use the best possible formation."
"Alex Ferguson gives a lot of advice to players and he's one of the best football coaches. He protected his players but he made me understand when I was making a mistake," said Beckham.
"If I play on Wednesday I won't be frightened but I will be excited because I played in that stadium for many years and I know what it means to be a Manchester United player. I know what it means for opponents to play there."
