Manchester United vs. A.C. Milan: It's Now Or Never For Milan Veterans

Tonight's biggest tie pits two teams at opposite ends of their lives against one another. Manchester United, full of youth complemented by one or two spots of experience, face an elderly Milan side, for whom the young Pato cuts a lonely figure amongst their elder statesmen.

The plot has been the same for Milan for a few years now. Their team is too old, their players no longer have the pace needed, they don't have anyone on the fringes threatening to break through.

But this year, there is a different air about them. An air of finality. Some players are simply at the end of their lifespan. Plus, being a World Cup year, 2010 is likely to see others making one last push to be recognised on the world stage before they fade.

Take Ronaldinho. He is currently back to something recognisable as his best, as he plows his one man furrow towards Dunga's world cup squad. The seleção boss hasn't picked Ronaldinho since the Beijing Olympics, and he has built a unified squad without him.

Ronaldinho is hoping that his irresistible form will force Dunga's hand. One has to wonder next season, with the World Cup carrot gone, whether he will be capable of such performances.

Likewise David Beckham, for so long the lynchpin of an underacheiving England side, is no longer even guaranteed a place in the squad, his ubiquity undermined by his move to the footballing backwater of Los Angeles.

This time last year, Beckham was in the middle of a hugely successful loan spell with the Rossoneri. Twelve months on, he is struggling to make an impact, having been used by Leonardo on the right side of a front three as well as in midfield.

His return to Old Trafford will fuel him tonight, but once the World Cup, one he admits will be his last, has passed, how much fuel will be left in his tank?

The Italian midfield duo of Andrea Pirlo and Gennaro Gattuso are also coming to the end of their lifespan. With a combined age of 63, this summer's tournament will also be the last chance for them to play in the biggest show on earth.

Of course, the Azzuri duo, along with Clarence Seedorf, have been there and done it all. Seedorf has won the Champions League five times with three different clubs, and Pirlo and Gattuso have won the World Cup.

But these are professionals, and not for one minute will their minds be on anything else this summer.

But once the winter draws in, how many will still have the desire to continue putting in the effort that is required of top footballers?

The effect of the World Cup on a player can be estimated by seeing the effect that it has had on O Fenomeno, Ronaldo, during his career. He burst onto the scene in 98, before breaking down in Milan, struggling with horrific injuries.

He eventually made a comeback, secured a move to Real Madrid, and hit the form of his life just before the '02 tournament in the Far East.

After enjoying arguably the most consistent four year stretch of his career since his move to Inter, the '06 World Cup passed and he slid from Real Madrid regular to unwanted, overweight has been by the time he rejoined Cruzeiro.

Of course, true to form, a spurt of goals has put him back in the frame for a World Cup place.

But nobody would bet on him being anywhere near the 2014 squad. Not even close. Perhaps not even playing football. He might not even see 2012.

And this is the worry for Milan. It has to be this year, because once the World Cup passes, they are going to have a huge rebuilding job to do. And that doesn't happen overnight. Look how long it took Barcelona between European Cup wins.

And because it has to be this year, it has to be tonight. All the ingredients are there for a classic.