"She's got a minor bone bruise and a grade 1 strain of the ACL," U.S. team spokesman Marc Habermann said Friday. "She fell and the ski wouldn't come off."
The injury occurred Thursday. Habermann could not immediately confirm which knee was injured.
Kildow will miss Friday's slalom and the team event that concludes the championships Sunday. She won two silver medals here in super-G and downhill.
"She had an MRI last night and they are re-evaluating her this morning," Habermann said, adding that there was also a possibility Kildow could miss some World Cup races after the worlds.
The women's World Cup circuit is due to resume with races in Sierra Nevada, Spain, Feb. 24-25.
Kildow's injury leaves the U.S. team depleted for Sunday's team event. Julia Mancuso, the other top woman on the American squad, left Are on Thursday to return home and rest up for the remainder of the World Cup season. Most of the men's speed team, except for Bode Miller, has also gone home.