When Lindsey Vonn made a promotional visit to Afton Alps last fall, the Burnsville native was presented with a giant card signed by hundreds of people who had come to see her. The Olympic champion in downhill skiing had just returned to the slopes after a serious knee injury, and among the messages of support and luck, one wary person wrote: Don't get hurt.

Vonn reinjured her right knee in November, and that led to a broken heart when she announced Tuesday that she will not compete at the upcoming Winter Olympics.

Vonn, 29, said via her Facebook page that she would soon undergo another knee surgery and hopes to compete in the 2015 world championships in her current hometown of Vail, Colo.

"I am devastated to announce that I will not be able to compete in Sochi,'' Vonn said in her Facebook post Tuesday morning. "I did everything I possibly could to somehow get strong enough to overcome having no ACL. But the reality has sunk in that my knee is just too unstable to compete at this level.''

Vonn tore the anterior cruciate ligament and medial collateral ligament in her right knee in a crash at the world championships last February. After intense rehabilitation, she returned to snow in late August, earlier than projected, and planned to return to competition in late November. She reinjured the knee when she crashed in training for that event in Beaver Creek, Colo., partially tearing the reconstructed ACL, but she missed only one weekend of racing.

Vonn competed at Lake Louise, Alberta, in early December. She then injured the knee again in Val d'Isere, France, spraining the MCL.

Bill Marolt, president of the U.S. Ski and Snowboard Association, said he expects Vonn will be able to return to competition. With a U.S.-record 59 victories on the World Cup circuit, she is three shy of tying the all-time record held by Annemarie Moser-Proell of Austria.

"In looking ahead, I have every ounce of confidence that Lindsey will be in the starting gate next World Cup season, ready to compete,'' Marolt said. "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.''

Her personal publicist, Lewis Kay, said in a statement that Vonn "will have surgery shortly," according to The Associated Press.

When Vonn returned to competition in December at Lake Louise, she finished well behind the leaders in two downhill runs and fifth in a super-G race. After skiing there, Vonn still sounded optimistic, declaring she would be in Sochi, "fighting for my medal."

But at Val d'Isere, France, on December 21, her knee gave out during a downhill run, causing her to miss a gate and be disqualified. The Associated Press reported at the time that she didn't fall, but grimaced as she pulled up and clutched at her knee.

Kay said Tuesday that an MRI after that episode "showed an MCL sprain, which coupled with the torn ACL, has made it impossible to stabilize her knee and be ready to safely ski again next month."

Over the weekend, U.S. ski team coach Alex Hoedlmoser said that Vonn had not trained on snow since the Val d'Isere incident.

Vonn was the World Cup overall champion from 2008 to 2010, and won the title for a fourth time in 2012.

Mikaela Shiffrin, the reigning world champion in slalom, and Julia Mancuso, a three-time Olympic medalist, will now be the American women with the best chance of stepping on the Alpine skiing podium in Sochi.

Shiffrin, the U.S. teenager who has been labeled the "next Vonn" by some, wrote on Twitter: "It's hard to swallow that @lindseyvonn won't be competing in Sochi, but I'm incredibly impressed at her determination. She's a true #hero."

Another American ski racer, Stacey Cook, posted on Facebook: "Bummed Lindsey Vonn. Our team is not the same without you. You leave big shoes to fill for the rest of the year. ..."

The Associated Press contributed to this story