The British rider was being airlifted to a hospital, Brailsford said at the Criterium du Dauphine race in southeastern France.
"He's hit a wall at 60 kilometres [per hour] or something like that".
Four-time Tour de France victor Christopher Froome is out of this year's race after a serious accident while training, his manager has confirmed to French television.
'He is now on his way to a local hospital and won't start today's fourth stage. "I am awaiting information and transport to get to where he is and as soon as we have any information we will update you". But in 2014 having started as the Tour's absolute favourite, Froome's dramatic crash-out following repeated falls in the rainsoaked first week left that year's Tour wide open.More news: Marvel's Avengers A-Day Could Change Character Designs After Fan Backlash
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This year's Tour de France embarks from Brussels on July 6 and the loss of the iconic four time victor will shake up ambitions at several teams.
In fact, five of the last seven winners of the Dauphine have gone on to top the podium in Paris - three of those occasions being Froome himself.
"He crashed in the downhill section of the course at high speed".
Chris Froome in the Tour de France yellow jersey. "He'll be helicoptered to either Lyon or Saint-Etienne hospital within a few minutes", said Brailsford. It is far too early to consider or predict timelines in terms of recovery but it's unlikely that Froome will race again this season given the recovery time other cyclists have needed for similar injuries.
Froome was eighth in the overall classification after three stages of the eight-day race, just 24 seconds behind leader Dylan Teuns. He also won the 2017 Vuelta a Espana and the 2018 Giro d'Italia, making him the greatest Grand Tour rider of his generation. Sport is full of history and legends. Long-time Froome teammate Geraint Thomas is the defending champion.