Lindsey Vonn of the US reacts in the finish area after a training session ahead of the Women's World Cup Downhill skiing race in Val d'Isere, French Alps, December 18, 2013.  [Photo/Agencies]

Less than two weeks after reconstructive right knee surgery in February 2013, Lindsey Vonn already was sounding a positive note, saying she was "really looking forward to Sochi" and defending her Olympic downhill gold medal.

Along the way to the next Winter Games, though, Vonn began facing more setbacks. As she'd move past one, another would surface. In the end, it was too much, even for Vonn, the most accomplished US ski racer in history. Expected to be one of the biggest stars at the upcoming Games, Vonn announced Tuesday _ exactly one month before the opening ceremony _ she won't be able to race in Russia.

In a Facebook posting, Vonn said she is "devastated" to miss the Olympics, "but the reality has sunk in that my knee is just too unstable to compete at this level."

Her personal publicist, Lewis Kay, said in a statement the 29-year-old from Vail, Colo., will have knee surgery again "shortly."

Like many in her risk-filled sport, Vonn has dealt with injuries often, particularly at major events. She withdrew midway through the 2011 world championships because of a concussion. She raced with a severely bruised shin at the last Olympics. She skipped a race at the 2009 worlds after slicing her thumb open on a champagne bottle. She hurt her knee in training and missed a pair of races at the 2007 worlds. She took a scary fall during training at the 2006 Olympics, then left the hospital to compete.

"She's come back. She'll be back," Vonn's father, Alan Kildow, said in a telephone interview. "You'll see a lot of Lindsey Vonn in the future."

Vonn left the 2010 Vancouver Games with two medals: the first Olympic downhill gold for an American woman, and a bronze in the super-G. She is also a four-time overall World Cup champion, by far the most recognized name in Alpine skiing at the moment - and, as it happens, the girlfriend of Tiger Woods.

Add it all up, and she would have been the focus of plenty of media coverage in Sochi, certainly a main character in NBC's coverage for a US audience.

"Lindsey gives you great promotional value, and she's an amazing athlete and an amazing story," said Gary Zenkel, president of NBC Olympics. "But there are amazing athletes that are going to be in Sochi, many of which we know, some of which we haven't identified yet."

To those in the world of skiing, there's no doubt about the sport's most important athlete of late.

"Without Lindsey Vonn, the races are just not the same," Canadian women's Alpine coach Hugues Ansermoz said last month. "She just attracts so much interest. When Lindsey Vonn is here, there are more people coming to watch the race, there is more interest on TV, more journalists are interested. And her relationship with Tiger Woods makes even more people interested."

More photos of Vonn and Tiger:

Woods and Lindsey Vonn announce dating

At New York fashion show

Aching Tiger anchors US triumph