Belarus 10th seed Victoria Azarenka has had hospital treatment at the US Open after collapsing on court in the first set of her second-round tie against Gisela Dulka of Argentina.
With temperatures climbing into the 90s Fahrenheit (30s Celsius) for a third staright day, Azarenka quickly fell 1-5 down after 34 minutes against her more experienced South American opponent.
The 21-year-old then suddenly collapsed behind the baseline after Dulko had smacked a forehand past her and received treatment for several minutes before retiring from the tie.
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She was taken away from the court in a wheelchair.
US Open referee Brian Earley said in a statment: "Victoria Azarenka retired from her match with headache-like symptoms.
"She was taken to a nearby hospital for diagnostic testing. Out of respect to her privacy we can not give any more details.
"However, we can say that this does not seem to be primarily a heat-related illness."
The player later explained that she had fallen in the gym prior to her match while running a sprint and had stumbled forward, hitting her head and arm
"I was checked by the medical team before I went on court and they were courtside for monitoring," she said.
"I felt worse as the match went on, having a headache and feeling dizzy. I also started having trouble seeing and felt weak before I fell.
"I was taken to the hospital for some medical tests and have been diagnosed with a mild concussion."
A former top junior, Azarenka is regarded as one of the best young players in the world at the moment and had been expected to make a run at the title here.
