TOKYO: Fresh from his breakthrough victory at the US Open last month, Juan Martin del Potro tops the bill in a depleted field at the Japan Open tennis tournament which gets underway on Monday.

The 21-year-old Argentine, ranked fifth in the world, came to Tokyo last year as a hot favourite, but finished runner-up with a injury problem in the final seeing him lose to Tomas Berdych of the Czech Republic.

This year, he returns as a Grand Slam champion after shocking world number one Roger Federer in five sets at Flushing Meadow last month.

To the disappointment of fans, Federer withdrew from this week's 1.2 million dollar tournament citing back and knee problems.

"I am disappointed that I have to withdraw. I decided to take the difficult decision to withdraw, so that I can give my body a chance to rest, rehabilitate and fully recover from a physically challenging year," said Federer.

Also out is Japanese teenage sensation Kei Nishikori due to a right elbow injury and Britain's Andy Murray with a wrist injury.

Top seed del Potro will take on a qualifier in the first round and then play the winner of the Leonardo Mayer-Jurgen Melzer clash.

Del Potro has been drawn in the same half of the field as defending champion Berdych, seeded five, the 2003 Japan champion Rainer Schuettler of Germany, and third seed Gilles Simon of France.

The 2008 Australian Open finalist Jo-Wilfried Tsonga of France leads the bottom half of the draw as the second seed and will play Mischa Zverev of Germany in the first round.

Tsonga's main rivals include Gael Monfils of France, seeded fourth, the Beijing Olympic doubles gold medallist Stanislas Wawrinka of Switzerland, seventh seed, and Radek Stepanek of the Czech Republic.

Richard Gasquet of France, the runner-up here two years ago, will have a chance to play Tsonga in the second round if he can beat Philipp Petzschner of Germany in his opener.