Vonn acknowledged the knee was too unstable for her return to the slopes .
Vonn , 28 , was forced to give up her Olympic hopes last month after reinjuring her surgically repaired right knee .
Vonn acknowledged the knee was too unstable for Vonn 's return to the slopes .
Vonn , 28 , was forced to give up her Olympic hopes last month after reinjuring her surgically repaired right knee .