Olympic downhill ski champion Lindsey Vonn has suffered a tear of her anterior cruciate ligament in a crash in training on Tuesday.
The 29-year-old, who sustained a similar injury in her right knee last February, was due to start preparations for next week's World Cup races at Beaver Creek, Colorado.
However, those plans have now been scrapped, leaving her battling to be fit for the Sochi Winter Olympics in February.
"Vonn plans to rest for a few days before pursuing physical therapy," read a statement from the US Ski Team.
"U.S. Ski Team medical director Kyle Wilkens reported her response to the therapy would ultimately determine the timetable for her return to active training."
The four-time World Cup champion is currently dating golf star Tiger Woods.