Downhill queen Vonn to miss Sochi Winter Olympics
USA's Lindsey Vonn arrives for training for the World Cup Downhill on December 18, 2013 in Val d'Isere, French Alps
"I am devastated to announce that I will not be competing in Sochi," Vonn said on her Facebook page.
"I did everything I possibly could to somehow get strong enough to overcome having no ACL (anterior cruciate ligament) but the reality has sunk in that my knee is just too unstable to compete at this level.
"I'm having surgery soon so that I can be ready for the World Championships at home in Vail next February.
"On a positive note, this means there will be an additional spot so that one of my teammates can go for gold."
The 29-year-old Vonn, who has 59 World Cup race victories to her credit and who is the reigning Olympic downhill champion, badly injured the knee while competing in a super-G at the World Championships in February.
After reconstructive surgery on the joint and a lengthy layoff, Vonn returned to World Cup competition at Lake Louise, Canada in early December, but only after she injured the same knee again while training in Colorado in November.
At Lake Louise, Vonn was 40th in the first downhill, 11th in a second downhill and fifth in a super-G.
She then competed in a downhill at Val d'Isere in the French Alps just before Christmas, under the watchful eye of boyfriend Tiger Woods, but failed to finish the race as she skied out.
"Unfortunately I have no ACL and it just gave out on me," she said at the time.
Vonn said she would compete in just one or two races before the Winter Olympics in the Russian ski resort of Sochi from February 7.
Her absence will deprive the Games of one of the biggest stars and draws in winter sport with her romance with Woods making headlines worldwide.
The head of the US Ski and Snowboard Association, Bill Marolt said that he was confident Vonn would be able to bounce back from the injury in time for the next World Cup season later this year.
"She knows the hard work it takes to get to the top and still has significant goals to achieve in what has been an incredible career.
"While Lindsey won’t be in Sochi, we have a strong team that is well prepared to challenge.
"The women’s speed team is experienced with five athletes who have achieved World Cup podiums and a seasoned veteran in Julia Mancuso who has won three Olympic medals in her career."
In a high-risk sport that leaves little margin between triumph and tragedy, Vonn has endured several injury nightmares in what has been a spectacular career.
She bounced back from a frightful crash in downhill training at the 2006 Olympics that left her with a badly bruised back, competing just days later.
A year later, a badly twisted right knee in slalom training at the Are world championships saw her season brought to a premature end.
Vonn also broke a finger in a crash at the 2010 Olympics in Vancouver, an event she went into carrying a shin injury.
Each time the American battled back, picking up multiple medals and four overall World Cup titles along the way.
It remains to be seen if, at 29, she will be able to pick up the pieces and once again be competitive at the highest level.