She sustained the injury in a crash Thursday on Copper Mountain, in Colorado.
"I had successful surgery (Thursday) night in Vail and everyone took great care of me," Vonn said in a Facebook post Friday.
"While I am beyond frustrated by this latest setback, at least my knees are OK and I will return to the slopes as soon as possible, as I always do! Thank you for the continued love and support, it means so much to me."
Vonn, the most successful woman in World Cup ski racing with 76 wins, suffered a nasty knee fracture in March
that ended her ski season.
The 31-year-old skier already had an extensive injury history, including the torn ACL/MCL and fractured tibial plateau she suffered during the World Championships in February 2013.
It is unclear how long the injury will keep Vonn off the slopes. She is currently 11 wins away from breaking the all-time World Cup record set by Swedish legend Ingemar Stenmark in 1989
Back on the slopes, Vonn's American team mate Mikaela Shiffrin won herself a Lapland reindeer after winning the first slalom of the season in Levi, Finland.
According to the US team site
, the reindeer is called Sven and is a companion for Rudolph which she won in 2013.
Shiffrin edged the race, finishing 0.67 of a second ahead of Swiss skier Wendy Holdener after the two runs.
Slovakia's Petra Vlhova was in third place but pushed Holdener very hard, beating her in the second run but not enough to overhaul the deficit form the first.
"The hill was in really, really perfect condition and it was a beautiful day," Shiffrin said after the two runs.
"I'm not unbeatable, I can tell you that," she was quoted as saying on the US team website. "So every race I have to be faster, and it's certainly not a comfortable position."
Shiffrin is still only 21 and already an Olympic and world champion. All eyes will be on her season as she adds downhill and super-G to the slalom where she has been so dominant.