Britain's four-time champion Chris Froome suffered a fractured right femur, a fractured elbow and fractured ribs in a high-speed crash that has ruled him out of the Tour de France.
The Team Ineos rider, 34, hit a wall at 54km/h when he took a hand off his handlebars to blow his nose, according to team principal David Brailsford.
The crash occurred before stage four of the Criterium du Dauphine.
Froome has been airlifted to St Etienne University Hospital for surgery.
"Even though we all recognise the risks involved in our sport, it's always traumatic when a rider crashes and sustains serious injuries," said Brailsford.
"Chris had worked incredibly hard to get in fantastic shape and was on track for the Tour, which unfortunately he will now miss.
"One of the things which sets Chris apart is his mental strength and resilience - and we will support him totally in his recovery, help him to recalibrate and assist him in pursuing his future goals and ambitions."
Froome was eighth overall in the Criterium after three stages of the eight-day race.
Ineos said Froome has "multiple serious injuries" after the incident, which occurred during a practice ride on Wednesday's 26.1km time-trial course in Roanne, France.
Speaking to BBC Sport's BeSpoke podcast: Brailsford said: "He came down a technical descent and onto a straighter piece of road with houses either side. He signalled to [team-mate] Wout [Poels] that he was going to clear his nose, he took his hand of the bar to do that and a gust of wind took his front wheel, he lost control and went straight into the wall of a house.
"We have had a look at his data, he went from 54km/h to a dead stop."
Froome would have been chasing a record-equalling fifth victory in the Tour, which starts in Brussels on 6 July.
He went into last year's race as favourite, holding all three Grand Tour titles, having won the Vuelta a Espana and the Giro d'Italia.
He finished third as team-mate Geraint Thomas became the third Briton to win the race.
Tom Fordyce, chief sports writer
Froome has been the dominant stage racer of his generation, his accident coming at a time when he was bookmakers' favourite to win back the Tour de France yellow jersey that he ceded to team-mate Geraint Thomas a year ago.
His entire year had been focused on three weeks in France in July, his determination to win a record-equalling fifth title obvious when BBC Sport's BeSpoke podcast went out to visit his training camp in Tenerife two months ago.
Ordinarily riders get up and race almost as soon as they crash. When their injuries are severe they immediately focus on a comeback race; cycling is a sport that waits for no champion.
But if Froome's injury is as bad as early reports indicate, not only the Tour but also the Vuelta a Espana in August and September's World Championships in Yorkshire must also be in significant doubt.