The reigning four-times overall World Cup champion was taken to hospital in Colorado, where she had been preparing for the giant slalom and slalom races in Aspen on November 24 and 25.
The American's ski technician Heinz Haemmerle said it is not the first time this season Vonn has visited hospital.
"She told me she feels bad and has pain all over her body and that her bones are hurting. She's been (to the hospital) two or three times. This is the first time she's stayed overnight," Haemmerle told AP.
"The coaches also don't know. First they told me we would train again Monday, then Wednesday, now the end of the week."
Vonn has not trained since racing the second run of the season-opening giant slalom in Soelden three weeks ago.
The 28-year-old missed last weekend's slalom in Levi in a bid to prepare for the upcoming North American events in Aspen and Lake Louise. The latter is her most successful stop of the FIS circuit.