Aussie Open tennis shapes up as survival of the fittest

Tennis's biggest stars are having to grit their teeth and play through the pain barrier as the grand slam season gets under way with a litany of aches, pains and absentees. With the Australian Open starting on Monday, all of the men's top four have either current or recent injuries, while fitness woes threaten to play havoc with the women's draw. Defending champion Kim Clijsters and five-time winner Serena Williams both pulled out of a warm-up event in Brisbane after on-court scares, while 2008 Open victor Maria Sharapova has not played this year due to an ankle problem. On Wednesday, 10th seed Andrea Petkovic withdrew with a stress fracture in her lower back, becoming the second high-profile cancellation alongside Venus Williams, who has auto-immune disease Sjogren's syndrome. And world number one Caroline Wozniacki was troubled by a wrist injury in her quarter-finals loss to Agnieszka Radwanska at the Sydney International, but a scan revealed the problem was not serious. Further withdrawals would inevitably throw the spotlight back on the busy tennis schedule, just months after men's players threatened to go on strike. Men's number two Rafael Nadal, 2009 champion in Melbourne, is one of the walking wounded, and is planning to take a month off in February to rest his troublesome shoulder and knee. Grand slam record-holder Roger Federer, 30, a four-time winner at Melbourne Park and not known for injury problems, pulled out of the Qatar Open with back spasms which he said were "not crazy-bad" but also "not very good". "Sometimes you just go through tougher moments," Federer said earlier. "It's also part of a good player, being able to put that aside and still play good tennis. I promise you I had a lot of pain throughout my career, and I've managed to play with it." Britain's Andy Murray grimaced with pain during his first matches of the year before shaking off a niggling knee problem to win the men's competition in Brisbane. But perhaps the biggest question mark is over men's champion Novak Djokovic, who enjoyed a 41-match winning streak and snapped up three grand slams last year before physically breaking down. The world number one won 10 of 11 finals in a campaign widely regarded as one of the best in history, tempered by four losses in the final few weeks of his season -- among only six all year. But the Serb recovered to end 2011 with victory at an exhibition event in Abu Dhabi, and said he was free of his shoulder and back problems. Clijsters will be desperate not to let hip spasms, which forced her out in Brisbane, mar her final Australian Open before she retires at the end of the year. And Serena Williams was training in Melbourne with strapping on her ankle, after suffering a painful sprain at the Brisbane event. However, Williams did not seem in the mood to let the problem end her campaign. "Pain is only temporary but quitting lasts forever," she tweeted.