The Australian's new book 'Up front: a season to remember" claims that separate from his 2009 pre-season crash that broke his leg and left shoulder, the Red Bull driver broke his right shoulder in another mountain bike crash whilst he led the 2010 championship.
It is believed surgery on the "skier's fracture", sustained while on holiday in Australia prior to the Japanese grand prix at Suzuka, was the reason Webber missed the recent Pirelli test in Abu Dhabi.
He confirmed: "I was riding with a great friend of mine. Suddenly, he crashed right in front of me and I had nowhere to go but straight through the ears of the horse!
"Suzuka is a brutal track so it was a blessing that the Japanese weather gave me an enforced rest day on the Saturday, and a pre-race (cortisone) injection helped too.
"In the end, we got through the weekend all right," said Webber, who finished second at Suzuka behind his teammate and eventual champion Sebastian Vettel.
In Korea, Webber's hopes took a major hit with his crash on the slippery track, before he finished second – again behind Vettel – in Brazil.
And at the Abu Dhabi finale last month, Webber was uncompetitive whilst Vettel won the race and title from pole position.
But Webber said in his official book that he does not attribute losing the title to his shoulder injury.
12/06/10 One possible reason why Mark Webber’s form in the crucial final four races of the season declined is a fractured shoulder from yet another mountain bike accident, shortly before the Japanese Grand Prix.
The 34 year old travelled back to Australia after the Singapore Grand Prix and went out on a mountain bike ride when he injured himself again. He was following a friend who fell and with nowhere to go, Webber crashed into him and fractured his shoulder.
He did not tell Red Bull team boss Christian Horner or anyone else in the team, aside from his trainer Roger Cleary. He was given cortisone injections before driving.
The revelation comes in Webber’s new book, “A season to remember", which has just been published in Australia.
At the time he was leading the world championship, with 202 points, 21 ahead of Fernando Alonso and 31 ahead of eventual champion Sebastian Vettel.