The 29-year-old tore her knee ligament as she fell during a World Cup giant slalom at Jasna in her native Slovakia in January.
The injury sidelined the Beijing 2022 Olympic champion for the rest of the season and the beginning of the current one.
"Petra is still experiencing discomfort in her knee, which is incompatible with full skiing load," her Nike Ski Team said in a statement.
"Comprehensive examinations revealed cartilage damage, which requires further specialised care."
Vlhova, who is undergoing an intensive five-week treatment, will undergo another round of tests in January.
"Not everything is going as planned, and Petra is not having the happiest time in this context," said Vlhova's Italian coach Mauro Pini.
"I expect we will know more about her ability to handle full load by the end of December," he added.
Pini also said that medical tests have "confirmed a very good condition of the operated segments of the anterior cruciate ligament and meniscus, as well as high knee stability".
Until her injury, Vlhova, a slalom and giant slalom specialist, was a serious rival for US legend Mikaela Shiffrin.
The 29-year-old American, who is eyeing an unprecedented 100th World Cup victory, is currently recovering from a puncture wound she picked up during a giant slalom at Killington in November.
