LOS ANGELES - The clock is ticking on American Lindsey Vonn's bid to defend her Olympic downhill title as the injured US star officially withdrew Friday from next week's World Cup stop in Beaver Creek. Vonn was due to return to racing at Beaver Creek for the first time since reconstructive surgery of her right knee in the wake of a crash at the world championships in Schladming, Austria, in February. But she crashed on a training run at Colorado's Copper Mountain on Tuesday, and suffered a partial tear of one of her reconstructed knee ligaments. "Lindsey is extremely appreciative of the outpouring of support and good wishes," her spokesman Lewis Kay said Friday. "While her rehab is progressing, she is not at a point where she will be able to ski next week."–AFP