BRISBANE, Australia — 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 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.

On Saturday, Williams sounded optimistic in a brief message to her nearly 2.4 million Twitter followers.

“Team Williams on way to Melbourne. I’m doing everything to heal up and winfromwithin,” she tweeted.