He is now on his way to a local hospital and won't start today's fourth stage.
Brailsford said Froome had been speeding downhill with teammate Wout Poels when a gust of wind blew him off track, making him hit a wall. "We will provide a further update in due course", Ineos said on Twitter.
The Mitchelton-Scott rider, 26, leads Belgian Dylan Teuns by four seconds following the 26.1km time trial in Roanne, France. "He's just going to get airlifted shortly to hospital, Saint-Etienne, maybe Lyon".
"It's a very serious accident".
"Chris was taken to Roanne Hospital where initial examinations confirmed multiple injuries, most notably a fractured right femur and right elbow", said Team Ineos' doctor Richard Usher. Riders don't usually win three-week Tours in their mid-30's and since Froome has already won all three of them, France, Italy and Spain, this could well signal the end of a fabulous career of stage-race riding.
"I am awaiting information and transport to get to where he is and as soon as we have any information we will update you".
The Briton was practicing on the course of today's time-trial in the Dauphine Libere race in the French Alps when he came off on a corner.
Ineos principal Dave Brailsford confirmed to French television that the four-time victor will not start the Tour next month following a harrowing, high-speed crash during a training ride ahead of the fourth stage at the Critérium du Dauphiné.
But all indications were that Froome had done enough to be Ineos' unofficial leader at the Tour, ahead of both Thomas and Bernal, as he aimed for an historic fifth title.
Tour de France director Christian Prudhomme was swift to wish Froome a speedy recovery. Sport is full of history and legends.