Lifelong Red Devils admits Tuesday night will be "emotional."
Beckham made his name with the Red Devils before leaving for Real Madrid in 2003 and admitted he remains a supporter of the club, meaning Tuesday night's clash will be an occasion to tug at the heartstrings.
"It is going to be an emotional game, but as a Manchester United fan, it's the first time I am going to want United to lose," he told reporters at a press conference on Monday.
"As an AC Milan player I want to beat Manchester United and to say that as a Man Utd fan is quite difficult."
Despite the personal resonance of the match for him, the England midfielder also insisted that his professional focus was very much on beating United and progressing the Champions League.
"As much as it is emotional for me personally, it is important that we win the game," he added.
"I am a Milan player and I want us to play well in the game and progress to the next stage."Keep up to date with all the latest Champions League news with Goal.com