The American, who has suffered several knee injuries in her career, later put a message on Instagram saying X-rays showed a hairline fracture. She will have an MRI scan on Monday.
"I will wait and see how I feel tomorrow to decide if I can race," Vonn wrote ahead of Sunday's super-combined race at the same venue. She also posted a picture of herself with her leg elevated and her knee wrapped up in a large ice pack.
The start of the race in Soldeu was delayed by three hours because of heavy snow and high winds. Winner Federica Brignone of Italy, who started with bib number eight, said she was lucky to get down the shortened course before more snow fell.
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"When I went down it was really good," Brignone said of the weather after finishing 0.13 seconds ahead of American Laurenne Ross. "It was not the best conditions for the best racers... but I took advantage of my luck."
Vonn, who started 16th, was followed down by her biggest rival Lara Gut of Switzerland, who skied a conservative race, finishing 1.15 seconds off the pace, and moved within eight points of Vonn in the overall competition.
(Reporting by Clare Fallon; editing by Ed Osmond and Ken Ferris)
