Formula One champion Michael Schumacher is fighting for his life after a skiing accident medics said he would not have survived had he not been wearing a ski helmet.
Doctors said the star remained in a critical condition after undergoing surgery for a severe head injury he sustained while skiing off-piste yesterday in the resort of Meribel in France.
The 44-year-old German and seven-times Formula One champion is now in an induced coma in intensive care.
Medics, speaking at a news conference earlier today, said the injury was "particularly serious" and refused to speculate on Schumacher's prognosis.
But they added that he would "certainly not" have survived the accident had it not been for his helmet.
Professor Jean Francois Payen, head of anaesthetics at the clinic where Schumacher is being treated, said there were no plans to carry out a second operation.
" This accident was particularly serious and he was dealt with immediately and at our hospital he was immediately operated on after a brain scan.
"And then afterwards his condition is critical. As for cerebral care, all the recommended treatments have been introduced and for the moment we are not able to express ourselves with regards to Michael Schumacher's future."
He said the driver's helmet had protected him to a "certain extent" from the "very violent shock".
"Taking into consideration the very violent shock, his helmet did protect him to a certain extent, of course. Somebody who would have this kind of accident without a helmet certainly, he would not have got to here," he said.
Professor Stephan Chabardes, the neurosurgeon who operated on Schumacher, said he had been admitted suffering from intracranial haematoma - blood clots - bruising and swelling of the brain.
" Mr Schumacher was taken by helicopter very quickly to Grenoble Hospital. On his arrival we examined him clinically and we realised he was in a serious condition, in a coma, with in fact cranial pressure," he said.
"The brain scan showed a number of pieces of information, some intracranial haematoma but also some cerebral contusions and oedema.
"We operated urgently to try to eliminate the haematoma. After the operation we saw that we had been able to eliminate these haematoma but also sadly the appearance of various bilateral lesions.
"So therefore he was taken to intensive care to try to help."
The hospital said that Schumacher was being kept in a state of hypothermia by controlling his temperature to keep it at 34C-35C (93.2F-95F). He is under general anaesthetic.
"Currently our objective is to reduce as much as possible any kind of external stimuli and to try to ensure he gets oxygen to his brain," a spokesman said.
"He arrived with lesions that were quite important so we think that in fact the shock seems to have taken place at high speed.
"Hour by hour we are going to try to gain time.
"But the treatment we are going to introduce, we know what we're hoping for but currently we are not able to give you any more information.
"We're not able to tell you what's going to happen as far as the future is concerned because it's too early to talk about it."
Schumacher's 14-year-old son was reported to have been with him at the time of the accident..
The star's manager, Sabine Kehm said in a statement: "Michael fell on his head when he was on a private skiing trip in the French Alps.
"He was taken to hospital and is receiving professional medical attention. We ask for understanding that we cannot give out continuous information about his health.
"He was wearing a helmet and was not alone. No-one else was involved in the fall."
The director of the Meribel resort was earlier quoted as saying the injury, which happened at 11.07am local time, was "not very serious".
Christophe Gernignon-Lecomte said on rmcsport.bfmtv.com: "It was a pretty heavy fall at 1100 this morning while skiing off piste. He was wearing a helmet. He was conscious after his fall.
"Two or three minutes later two ski patrol intervened to help him. They immediately asked for a medical evacuation helicopter. It arrived in less than 15 minutes. He was sent to Moutiers first, then on to Grenoble for more analysis."
The accident has revived memories of actress Natasha Richardson who died in 2009 after suffering a serious head injury in a fall while skiing at a Canadian resort.
Initially she had not seemed to be seriously injured following the accident during a skiing lesson at the luxury Mont Tremblant resort in Quebec.
Schumacher has received an outpouring of support from the racing world, including from British F1 former world champion Jenson Button, who urged him to pull through.
"My thoughts are with Michael Schumacher at this tough time. Michael, more than anyone, has the strength to pull through this," he tweeted.
Schumacher's injuries have caused particular shock in his native Germany. Fellow German-born sports star Boris Becker called on Twitter for prayers for a "full and speedy recovery" for the F1 champion.
German chancellor Angela Merkel said she was "extremely shocked along with millions of Germans" to learn of the accident.
Schumacher retired from F1 for the final time in 2012 after a three-season comeback with Mercedes.
Schumacher, who also raced for Jordan, Benetton and Ferrari, won the last of his world titles in 2004.
He won two with Benetton in 1994 and 1995 before moving to Ferrari and winning five in a row from 2000. The German has 91 career wins.
His return to the sport with Mercedes after a spell in retirement was less successful. He managed just one podium finish in his three years with the team and a best end-of-season placing of eighth in 2011.
During his first period of retirement, in 2009, he was taken to hospital after a motorbike crash during testing at a circuit in Cartagena, Spain. He did not suffer serious injuries on that occasion.
Meribel, an upmarket resort, hosted the ice hockey and women's alpine skiing at the 1992 Winter Olympics.
Ms Kehm later issued a statement on behalf of Schumacher's family thanking medics and well wishers from across the world.
"We would like to thank the medical team who we know do everything possible to help Michael," it said.
"We like to also thank the people from all around the world who have expressed their sympathy and sent their best wishes for Michael's recovery.
"We would like to ask the media to respect the privacy of us and our friends and thank them for their support."