Investigators into the ski accident which left retired Formula One racing driver Michael Schumacher in a coma are inspecting a camera which was fixed to Schumacher's helmet. Eyewitnesses to Sunday's accident are also being questioned, including Schumacher's 14-year-old son.

News agency AFP reports a source close to French authorities revealed the existence of the camera late on Friday, confirming reports from French newspaper Dauphine Libere.

Meanwhile, several dozen fans, many wearing gear from Ferrari, one of Michael Schumacher's former Formula One teams, gathered outside of the University Clinic in Grenoble, France on Friday to mark his 45th birthday.

Many had travelled for hours to express their support for their driving hero.

"For us Ferrari fans, we are just like brothers, we are just one," one of the fans, who said he had spent four hours on a bus from Italy to be there, told the Reuters news agency. "We are here to celebrate and to celebrate his battle for life."

"With all the joy he has given us, it was important for us to return the favor and be here for Michael," said another Italian fan.

"At the moment, he is tackling the most important fight of his life and therefore we want to send him very special wishes," a statement posted on the website of the Ferrari team said.

"There have been so many wonderful moments we have spent together and we have chosen 72. It's not a random number, as it represents the number of wins Michael achieved with the Scuderia from 1996 to 2006: 72 Grands Prix that gave us and the millions of Prancing Horse fans from all over the world so much pleasure," the statement added, referring to the horse that is part of the company's logo.

Schumacher is credited with helping return the Italian team to dominance on the Formula One circuit between 2000 and 2004, winning five consecutive drivers' championships. Prior to his arrival, the last Ferrari driver to win a title had been Jody Scheckter in 1979.

The former driver, who was born in the town of Kerpen, near the western German city of Cologne, has been receiving treatment at the Grenoble hospital since he fell and hit his head on a rock while skiing off-piste at the Meribel ski resort on Sunday.

'Critical but stable'

There has been no official update of his condition since Wednesday, when his long-time manager Sabine Kehm told reporters he was critical but stable.

Schumacher has been in an induced coma since doctors conducted two operations to remove bleeding and relieve pressure on his brain which developed as a result of the accident.

His wife Corinna, their two children, his brother Ralf and father Rolf as well as close associates have spent much of the time since the accident at his bedside.

The family used a statement posted on its website to thank well-wishers for their support.

Schumacher was wearing a helmet when he fell, but a source close to the investigation into the cause of the accident said the impact was so great that it caused the helmet to split into two.

Schumacher was Formula One's most successful driver of all time, having won 91 Grand Prix races and seven drivers' championships during a career that spanned the better part of two decades.

pfd/kms (AP, Reuters, dpa)