The two clubs face off in the first leg of the Champions League Round of 16 at the San Siro and it marks a special occasion for Beckham, who has never played against the club which helped make him the biggest name in the sport.
But he is not planning a welcoming home, rather is keen to help his Italian club record a big victory over the reigning English champions.
"This is an emotional time for me," Beckham said.
"I have never played against Manchester United before in the seven years since I left the club.
"So this is the first time I am going to want Manchester United to lose. It is a strange feeling but I am a Milan player and I want us to progress to the next stage of the Champions League."
Despite these comments, Beckham confirms he will not celebrate if he was to score, out of respect for the United players and fans.
"I would be pleased to score, of course, and if I do, it would be amazing," Beckham added. "But out of respect for Manchester United and their fans, I would not celebrate.
"I don't want the Milan fans to think I wouldn't be excited, though. It's just that I spent a long time at United and the fans were always brilliant with me. I want to repay them with my respect."