Serena Williams' preparations for the Australian Open were thrown into disarray last night when a persistent knee problem flared up again, forcing her to retire hurt in a warm-up event and prompting speculation about her future.
The World No.1 had to retire midway through her match against Australia's Jarmila Wolfe in the Hopman Cup mixed-team event. She also pulled out of her first match on Monday because of the same problem.
She will reassess her fitness on a daily basis, but with the year's opening Grand Slam only 12 days away, she will need to recover quickly if she is to make a successful defence of her title in Melbourne.
Patrick Mouratoglou, her coach, revealed afterwards she has been having injections in her knees every six months because of the wear and tear to her cartilages. He said she was usually able to play within two days of the procedure, but after the latest injection last week, her left knee had become inflamed.
"It's important now to take the right decisions, because it's not only the Australian Open that's important, it's all the preparations you do beforehand," Mouratoglou said. "Serena has to be able to run and do everything necessary to be ready, which she cannot do at the moment."
This was Williams' first appearance since her crushing disappointment at the US Open in September, when defeat in the semi-finals ended her hopes of becoming only the fourth player in history to win all four Grand Slam titles in the same year.
The 34-year-old already holds the Open era record as the oldest women's Grand Slam champion and World No 1. She took a break at the end of last season because she felt she needed a rest both mentally and physically.
She admitted her knees had been troublesome last year but added: "Mostly it was my whole body. The whole year was just great, but it was also physically very difficult. But that's all behind me now. I'm just really looking forward to this year."
The American hoped that "a little rest and a little treatment" would cure her current problem. "I've been training really hard during the off-season, really pushing myself beyond the limits," she said. "I just think a day off or two will make a world of difference."
Williams' discomfort was clear from the moment she lost eight of the first nine points. She eventually quit when trailing Wolfe 7-5 2-1.
"Usually I'm super-fast and I wasn't moving the way I wanted to," she said. "I was afraid to move. I need to get in that space where I am not afraid and then I will be able to move better. Speed is my strength."
The American team of Williams and Jack Sock cannot qualify for Saturday's final but are due to play the Czech Republic tomorrow. Williams did not rule out playing in that match and was optimistic. "It's just a minor thing in the road and I'm going to fly over it," she said.