Downhill world champion Aksel Lund Svindal could miss the entire ski season after tearing his Achilles tendon playing football.
The Norwegian Ski Federation confirmed he sustained the injury on Saturday.
Writing on his Facebook page, the 31-year-old said he was "playing around with a ball" after a training session when he "felt something snap".
The men's World Cup season starts with a giant slalom in Soelden, Austria, on Sunday, 26 October.
The season also includes the world championships in Vail and Beaver Creek in Colorado in February, where Svindal was set to defend his downhill title.
He has undergone surgery and is "probably out for the whole season", according to Claes-Tommy Herland of the Norwegian Ski Federation.
Svindal added: "A real injury and extremely bad timing just as the season is about to start. Nobody can say 100% sure how long the recovery will take, but I'm ready for the weeks that are coming."
Svindal won the overall title in 2006 and again in 2009 - after missing most of the 2007-08 season following a serious crash in training. He has 11 medals at major championships, including three at the 2010 Vancouver Winter Olympics.
He was the closest challenger last season to Austria's Marcel Hirscher who clinched his third straight overall title.