BRISBANE, AUSTRALIA (AP) - Serena Williams has a badly sprained left ankle, Roger Federer an aching back and Kim Clijsters a sore left hip.
Add in a limping-but-"I'll be OK" Andy Murray, Rafael Nadal playing with a sore left shoulder from the end of last season and the advance tournaments for the Australian Open are beginning to look like a star-studded hospital waiting room.
Williams' injury seems to be the most serious of the bunch, and could affect her chances of winning the singles title for the sixth time at Melbourne Park. She rolled over on it badly in the second round at the Brisbane International and pulled out of the tournament several hours later.
In her first tournament since losing the U.S. Open final in September, Williams was serving for the match against Bojana Jovanovski when she twisted her ankle and crashed heavily to the court.
After receiving medical attention, she limped through the end of that game and the next to complete a straight-sets win. She later withdrew after medical scans "confirmed that I have a left ankle sprain (and) that I probably shouldn't play on."
Federer and defending Australian Open champion Clijsters both withdrew from their tournaments Friday. Federer, a four-time Australian Open singles champion, withdrew ahead of his scheduled Qatar Open semifinal against Jo-Wilfried Tsonga because of a muscle spasm in his back, but said he expects to be fit for the first Grand Slam of the season when it begins on Jan. 16.
The 16-time Grand Slam singles champion said his back had not improved since beating Andreas Seppi in three sets Thursday.
Clijsters was forced to retire from her semifinal match against Daniel Hantuchova at the Brisbane International. Clijsters won the opening set 7-6 (4) but surrendered a break at the start of the second set and needed treatment after the third game. She came back on court for one game before walking to the net and telling Hantuchova she couldn't continue after falling behind 3-1.
Hantuchova has had an abbreviated run into Saturday's final, getting a walkover in the quarterfinals when 13-time Grand Slam winner Williams withdrew.
Both Clijsters and Williams, the 2010 Australian Open champion, were playing their first tournaments in four months. Clijsters struggled with injuries last season and only played eight tournaments, including the win at the Australian Open that helped her return to the No. 1 ranking for one week.
She said her hip had started to go into spasm during the match and she withdrew to avoid a serious rupture.
"I felt my left hip was getting tighter and tighter to the point I couldn't move forward with my upper body," she said. "So it was the smartest choice to try and not let it get any worse, to be ready for Melbourne."
The 28-year-old Clijsters, who has won three Grand Slam singles titles since returning from time out of the game to have a baby in 2008, said she was hopeful that medical scans Saturday would give the all clear to compete in Melbourne.
Players have complained in the past that the Australian Open is too early in the season, with most having limited tournament play after the offseason. The heat in the Australian summer is another issue and the predominance of hard-court tournaments is often cited as contributing to injuries.
"Oh, it's definitely more demanding," Clijsters said about the hard courts, but "I think every surface has their advantages and disadvantages.
"It's just _ our sport has evolved into such a strong sport where physically _ I mean, it's so much more demanding on the body and how we play."
Clijsters said players were spending more time in the gym to build strength to cope with the increasing demands on their bodies and many traveled with a physical therapist.
"When I came on tour ... nobody was hardly ever in the gym besides warming up with a skipping rope or doing some shoulder exercises and now there's everybody _ because it's necessary," she said. "The tennis that I play is physically so demanding on the body and then ... combine that on a hard court."
Murray, who will play in a men's semifinal at Brisbane on Saturday, dropped the opening sets in his first two rounds as he overcame soreness and stiffness from the offseason. He breezed through a quarterfinal against 2006 Australian Open finalist Marcos Baghdatis and said he's feeling OK now.
Nadal, who has struggled with a sore left shoulder, was beaten in straight sets by Gael Monfils in the Qatar Open semifinals on Friday, but did not blame any injury problems for the loss.
There have been several other injury pullouts. Sixth-seeded Alex Bogomolov Jr. of Russia withdrew from Qatar with a right ankle injury. At Brisbane, Florian Mayer retired with a groin injury and Tommy Haas with a calf muscle injury.
Maria Sharapova withdrew before the Brisbane tournament with an injured ankle and Venus Williams announced in mid-December that she was pulling out of the ASB Classic in Auckland, New Zealand, which was supposed to be her first competitive match since August. The 31-year-old Williams is still recovering from the immune system disease Sjogren's syndrome, which can cause fatigue and joint pain.
There has been no word on Venus' status for the Australian Open. Her sister's fitness for Melbourne may also be in doubt until just before the tournament starts.
"I'm going to take a couple of days off _ not too many _ and see how I feel," Serena Williams, the 2010 Australian Open champion said after her withdrawal at Brisbane. "I'm still hopeful of playing the Australian Open."