World number three Andy Roddick [Images] has become the latest withdrawal from the Tennis Masters Cup, a lower back injury forcing the American to miss the season-ending eight-man tournament starting in Shanghai on Sunday.

Roddick's decision was confirmed on the ATP Tour's official Web site on Wednesday, just 24 hours after Australian world number four Lleyton Hewitt [Images] said he would skip the tournament as his wife was close to giving birth to their first child.

Roddick sustained the injury during his quarter-final match against David Ferrer at the Paris Masters last Friday and the 23-year-old's place in the draw has been taken Argentine world number 12 David Nalbandian.

"Though I have tried to continue with practice, the lower back spasms continue," Roddick was quoted as saying on the Web site.

"After being evaluated by medical staff upon my return to the United States, it is now clear that I am not able to resume tennis activities for 10-14 days.

"I apologise to the loyal fans and sponsors that have expected my participation in the Masters Cup. It is an honour for me to have qualified for this event for the third straight year.

"I realise the tremendous amount of time and effort the ATP and the Chinese government have spent on the event, and know it will be a huge success.

"I look forward to getting healthy, starting my off-season workouts for the 2006 season, and working towards qualifying for Shanghai next year."

Nalbandian also played in the 2003 Masters Cup and he is the third Argentine to qualify for this year's event, joining Guillermo Coria and Gaston Gaudio, who replaced Hewitt on Tuesday.

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