Russian ski cross racer Maria Komissarova has undergone major surgery after breaking her spine during training in Sochi.
The 23-year-old sustained a fractured vertebrae with a dislocation during practice on the ski cross course.
Komissarova was transported to a hospital close to Rosa Khutor Extreme Park where she underwent an emergency six-and-a-half hour operation.
She was due to compete on Friday but will now take no part in the Games.
"Maria Komissarova received a serious injury today during training. She was urgently taken to hospital," the Russian federation said in a statement.
"Doctors carried out the necessary examination and took the decision to operate on her on the spot."
Ski cross is an event in which skiers race down a mountain against each other while negotiating big-air jumps and obstacles. The discipline was added to the Winter Olympic programme in 2010.
International Olympic Committee president Thomas Bach said it was a sport "with a certain risk".
He added: "You will never be able to exclude every kind of risk - we feel very sorry for the athlete.
"We hope that the operation will be successful and that she will be back."
In 2012, Komissarova became the first Russian woman to win a World Cup medal in ski cross when she finished second in the event at Grindelwald, Switzerland.
She was then unable to compete for six months of 2013 after having surgery on a leg injury.
Komissarova's crash marks the first serious athlete accident of the Sochi Games.
In 2010, the Vancouver Winter Olympics began in tragic circumstances when Georgian competitor Nodar Kumaritashvili died in a crash during a training run on the day of the opening ceremony.