The 16-year-old Hingis will not play for at least three weeks, which cover tournaments in Hamburg, Rome and Berlin, and there is a question mark against the French Open - the second Grand Slam of the season, which falls just a month before Wimbledon.
"So far it is certain that Martina will have to miss Hamburg, Rome and Berlin," said Melanie Molitor, Hingis' mother and coach, who added that it was possible that her daughter would not play in the French Open from 26 May to 8 June. Withdrawal from Paris would leave Hingis with little time to get match fit for Wimbledon.
Hingis was able to stand and joke after Monday's fall, but the next day she was unable to straighten her left leg.
Hingis was examined by specialists near her home in Switzerland before having arthroscopic surgery for a partly-torn ligament in Austria. "I'm relieved that my knee isn't that badly injured," she said.
Last January, Hingis escaped unhurt when she fell from a horse in Australia before going on to win the Australian Open.
Although it would seem unwise for Hingis to risk her career, Molitor has always insisted that her roller-blading daughter lives as normal a life as possible. "Martina's tennis is only possible because she doesn't just have tennis balls at the centre of her life," she said.
Five more seeds lost in the Monte Carlo Open yesterday. Jim Courier, Thomas Enqvist, Wayne Ferreira, Marc Rosset and Alberto Berasategui followed Pete Sampras, Thomas Muster and Boris Becker out of the clay-court tournament.
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