Red Bull's Mark Webber was driving with a broken shoulder for the final four races of the season, it has emerged.
The period coincides with a dip in form in which Webber lost his championship lead and then the title, which went to his team-mate Sebastian Vettel.
The Australian has revealed the injury, sustained in a mountain bike accident, in his new book, which has just been published in Australia.
Webber is refusing to blame the injury for his failure to win the title.
He also kept it secret from his team boss Christian Horner, only telling his physio Roger Cleary and F1's chief medical officer Gary Hartstein.
Webber sustained the injury after the Singapore Grand Prix.
The fracture was quite fine and could not be treated. Webber had cortisone injections before the races in Japan and Korea to dull the pain.
It is the second time in a little less than two years that Webber has suffered an injury while out training on a mountain bike.
In November 2008 he was hit by a car while taking part in his own adventure challenge in Tasmania and suffered a major fracture of his right leg as well as a broken shoulder.
On that occasion, he also kept the shoulder injury from his team and the public.
Webber says in his book, 'Up Front - 2010, A Season To Remember': "On the Sunday morning before (the Japanese Grand Prix at) Suzuka, I got on a mountain bike for the first time since my accident in Tasmania at the end of 2008.
"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!
"I suffered what they call a skier's fracture to my right shoulder.
"Suzuka is a brutal track so it was a blessing that the Japanese weather gave me an enforced rest day on the Saturday (when qualifying was rained off), and a pre-race injection helped, too.
"In the end, we got through the weekend all right."
At the time of his latest accident, Webber was leading the world championship by 11 points from Ferrari's Fernando Alonso and was 21 ahead of Vettel.
He finished second to Vettel in Japan, where the German was only 0.07 seconds faster in qualifying.
But Webber's title hopes took a major hit at the subsequent race in Korea, when he crashed on the second racing lap. Alonso won the race, which leapfrogged him over Webber in the championship and into an 11-point lead.
Webber then finished second to Vettel in Brazil before losing any hope of regaining the lead with an uncompetitive performance at the final race in Abu Dhabi.