(Reuters) - Overall World Cup leader Lindsey Vonn declared her Alpine ski season, and title hopes, over on Wednesday due to a knee injury.
Vonn, who had been chasing a fifth overall title, led Switzerland's Lara Gut by 28 points in the overall standings after last weekend's races in Andorra, where she crashed.
The decision was one of the toughest of her career but scans had shown a hairline fracture to be more serious and extensive than thought, the 31-year-old American said in a statement.
Further damage "could result in a serious surgery that would risk my future in ski racing," she said on her Facebook page.
The American won a record 20th World Cup trophy last month when she clinched the downhill crown. She has won 76 World Cup races, chasing Swedish great Ingemar Stenmark's record of 86.
"When I crashed on Saturday in Andorra, I fractured my tibial plateau," the skier explained of that fall in a Super-G race that damaged her left knee.
She was taken off the slope on a sled after receiving medical attention next to the course.
"The traditional X-rays that were taken that afternoon showed a hairline fracture, but the tibial plateau appeared to be stable and did not pose significant risk to competing. So I raced on Sunday."
Vonn -- whose career has been punctuated by serious injuries -- skied with a knee brace in that combined event. "No-one can ever call me a wimp," she had declared on Twitter afterwards.
On Wednesday, she said more precise scans carried out in Barcelona had made clear the risks involved in competing in any further races.
The images had revealed that, instead of one hairline fracture, there were three breaks that were "not sufficiently stable to permit me to safely continue skiing."
"With the World Championships in St. Moritz next year and the Winter Olympics in South Korea the following year, I cannot take that risk," she said.
Vonn, Olympic downhill champion at the 2010 Vancouver Games and also a former Super-G world champion, was robbed of her chance to defend her Olympic crown at Sochi in 2014 after requiring two operations on her right knee.
The American said she was proud of what she had achieved this season, with nine World Cup victories and setting records for the most World Cup downhill wins and Super G podium appearances.
Reporting by Alan Baldwin; Editing by John Stonestreet and Alexander Smith