Levered into an already overcrowded and much-maligned competitive calendar, the importance of the Olympic tennis tournament has always split top stars since its re-introduction to the Games in 1988.

This year's event in Beijing is no exception. American Andy Roddick is currently the highest profile definite absentee.

"It just comes to the point where the schedule is too long without the biggest sporting event in the world shoved right in the middle of its busiest part of the season," Roddick says.

Ask Chile's Nicolas Massu and you are likely to get a different answer. Massu was the unexpected winner of the doubles gold medal alongside Fernando Gonzalez in Athens. One day later, he claimed the singles title too.

"These are the best two days of my life," said Massu afterwards. "I just can't believe it. It's just too much to win two gold medals in two days. It's unbelievable for my country."

Massu joined a largely surprising list of men's winners, with the likes of Miroslav Mecir and Marc Rosset having also clinched gold medals where Grand Slam titles eluded them.

But the underdogs may struggle to have their day this time around. Roddick and his US team-mate Mardy Fish apart, most of the sport's big names are heading to Beijing in search of glory.

World number one Roger Federer says: "For me it is a very big tournament. I've won three of the four majors and the Masters Cup. The Olympics definitely rank on a Grand Slam level."

Andy Murray, who might have been expected to pull out given the catalogue of recent injury problems he puts down to his cramped schedule, added: "It's something not all athletes get the chance to do. It's an honour."

The women's event has tended to go more by the formbook, with gold medal victories for respective world number ones like Steffi Graf, Jennifer Capriati, Lindsay Davenport, Venus Williams and Justine Henin.

This year, however, there is much more scope for a surprise winner following the surprise retirement of Henin and the failure as yet of any of her rivals to step up and establish themselves as a clear successor.

Maria Sharapova, Ana Ivanovic and Jelena Jankovic will no doubt head to Beijing as favourites but it would be no surprise to see a rather lesser known star - perhaps Dinara Safina or Anna Chakvetadze - going all the way.

Victory can be expected to bring unimaginable joy, not only for some of sport's highest-paid stars but for their nation. The much-decorated Andre Agassi, who won the 1996 tournament on home soil, says it all.

"To win a grand slam in the sport of tennis is the biggest thing you can accomplish in your sport," said Agassi after beating Sergi Bruguera in the final.

"But the Olympics is the biggest thing you can do in all sports.

"To win a gold medal is what it's all about. I'll keep this over all of them. This is the greatest accomplishment I've ever had in sport."