The stadium in which Beckham became a star will resound to the singing of his name and chants of "Fergie, Sign him up". Even in defeat United are strong favourites to progress after their 3-2 first leg win in the San Siro Beckham will wear that distinctive grin. He won't be the only one: this is a feel-good event.
Related ArticlesSport on televisionWolves 0 Man Utd 1Red Knights receive Ferguson boostThe Red Knights' shot at buying Man Utd looks high, wide and hopefulFerguson: Rooney to blame for injuryFerguson backs Owen to returnWhy is Beckham loved so unconditionally? After all, as has been pointed out many times, he is not exactly a stranger to the kind of misbehaviour that has left John Terry and Ashley Cole as public pariahs.
The answer lies in his authenticity. It's ironic that a man whose image is projected on millions of screens and billboards should be admired for being the real thing.
The effect he has on people is startling. Whether it's young kids or world leaders, people respond instinctively to his charisma.
His role in helping secure the London Olympics is well known and at the World Cup draw in Cape Town in December he single-handedly put England's dysfunctional World Cup bid back on track.
On away trips with England you see the way his very presence transfixes people: in Kazakhstan his every appearance resulted in him being mobbed. People just wanted to touch him. It's a platitude to call him an icon but that is what he is, an icon for the religion of celebrity.
His authenticity is reflected in the way he plays his football.
Even in his pomp, a decade ago, he has always only ever been a good, rather than a great, player. His limitations and how he tries to transcend them compensating for a lack of pace with work-rate only endears him further.
Whether it's at Old Trafford or at Wembley, football crowds respond to him.
Football fans are a largely cynical bunch and great detectors of fraudulence so they will ignore the saccharine nostalgia and the sentimental clichés on Wednesday night and celebrate Beckham with uncharacteristic sincerity.
One man, though, is famously immune to all this: Sir Alex Ferguson. He is still tetchy when it comes to Beckham and in the build-up to this game has grumbled about "the David Beckham media circus". Even in praise there is damning faintness.
"He'll get a good reception and he deserves that," said Ferguson. "In my time here all of our former players have had a good reception, apart from Incey, who played for Liverpool and that's understandable." The implication is clear: Beckham is just another former player.
While there has been a détente in relations in the last few years he still refuses to speak about Beckham with real enthusiasm. When, last week, he was encouraged to expand on the subject of Beckham's time at United he responded with a curt "I'm not going into that." Why the reluctance?
Beckham certainly embarrassed Ferguson in the final months of his time at Old Trafford, pointedly parading the cut above his eye that Ferguson had inflicted by kicking a boot in the changing room after an FA Cup defeat against Arsenal.
Ferguson was also uncomfortable with the way Beckham's celebrity status was growing in the last couple of years before he left for Real Madrid in 2003. Perhaps he still resents the way Beckham usurps the agenda, no matter what it is.
Is there also a part of him that thinks he made a mistake in letting Beckham go? Ferguson is an autocrat. That's how he has built his success. He brooks no insubordination and Beckham's public charisma was making him impossible to control.
The moment Ferguson shows weakness the whole edifice comes tumbling down, so Beckham's continued presence in the Old Trafford dressing room was intolerable. It must have frustrated him, because he ended up missing out on at least two seasons of Beckham at his peak.
These days that talent is faded. Obviously he still strikes the ball with that distinctive snap and rip and plays with the old intensity but his lack of mobility is the problem.
At first Leonardo, the Milan manager, played him on the right side of the front three, which gave him a lot of freedom, but against United in the first leg he was pulled back into the central midfield trio. Really Beckham still works best as a right-sided midfielder in a 4-4-2. The problem is that formation is something of an anachronism at the elite level these days.
Still, Leonardo would be advised to start Beckham on Wednesday night, and not just out of a sense of occasion. Milan need to score at least twice and Beckham offers far more attacking threat than either Massimo Ambrosini or Rino Gattuso in midfield. His long, cross-field passes and dead-ball delivery will be a valuable source of chances.
Fabio Capello will be a rapt observer. The whole reason Beckham is even playing in this game is because he wanted to prolong his England career to this coming World Cup.
The project has been a success from that perspective as Capello has pretty much decided to take him for the effect his professionalism has on the rest of the squad alone. What he will be able to judge on Wednesday is Beckham's continued capacity to compete against the very best.
One last heroic Old Trafford performance and Beckham could well find himself with a bigger role to play for his country this summer.