Michael Schumacher, the greatest champion in the history of Formula One, was in a coma fighting for his life Tuesday after sustaining serious head injuries in a skiing accident in the French Alps.
Doctors have warned it is touch-and-go for the German racing legend as they wait for the full extent of his injuries to become clear after he fell and slammed his head on a rock while skiing off-piste on Sunday.
News of the accident stunned the Formula One community and racing stars joined German Chancellor Angela Merkel and legions of fans in expressing their hopes for his recovery.
Doctors at the hospital in the southeastern city of Grenoble where Schumacher is being treated said on Monday their famous patient was fighting for his life after suffering major brain trauma.
"He is in critical condition, his condition can be described as life threatening," Jean-Francois Payen, head of the intensive care unit, told reporters.
Payen said he had been placed in an artificial coma to limit the impact of his head injuries on his brain.
Doctors said it was too early to say whether Schumacher, who is due to turn 45 on January 3, would pull through.
"It usually takes 48 hours, or even longer, to be able to formulate an opinion" on injuries of this severity, said neurologist Jean-Luc Truelle.
The coma reduces the patient's temperature to around 35 degrees Celsius (95 degrees Fahrenheit) to reduce swelling. By being unconscious, the brain is also switched off to sounds, light and other triggers that cause the organ to use up oxygen as it processes the stimuli.
Schumacher's condition was initially described as non-life-threatening after he was helicoptered off a mountain in the upmarket Meribel resort after the accident.
However it quickly deteriorated and he fell into a coma.
Stephan Chabardes, who operated on Schumacher, said the former racer arrived in hospital Sunday in an agitated state -- his arms and legs jerking uncontrollably -- and was not able to answer questions.
Payen said Schumacher had been operated on immediately and had suffered "serious and diffuse brain lesions". Doctors do not expect to perform a second operation.
He added that Schumacher would not be alive if he had not been wearing a helmet.
"Given the violence of the impact, his helmet partially protected him. If someone had had this type of accident without a helmet, they would definitely not be here," Payen said.
Schumacher's wife Corinna and the rest of his family have thanked well-wishers and gave a special nod to the doctors treating him.
"We would like to thank the medical team who, we know, do everything possible to help Michael," Corinna said in a statement.
Schumacher's 'most difficult race'
News of the accident made waves, shocking fans, racing stars and leaders alike.
Damon Hill, who fought several memorable on-track battles with Schumacher, said he was "praying" for his former rival.
Merkel was "extremely shocked" by the incident, her spokesman Steffen Seibert told reporters.
Formula One quadruple world champion Sebastian Vettel, 26, who has said Schumacher was his childhood idol, said: "I am shocked and I hope that he'll be feeling better as soon as possible.
Schumacher is to driving what Einstein is to intelligence... So few people in human history whose names can be used as legit adjectives— Sahil Rizwan (@SahilRiz) December 31, 2013
Michael Viehmann, president of a Schumacher fan club in the small German town of Kerpen where the retired racer grew up, said fans were "very upset".
"We know him really well. He's a fighter, we're crossing fingers that he will win this battle," he said.
Schumacher, who won the last of his world titles in 2004, towered over the sport since his debut in 1991, winning more Formula One world titles and races than any other. He had a record 91 wins and is one of only two men to reach 300 grands prix.
Still hoping Michael Schumacher can pull through...it's sad that barely no one here in America knows who he is. #Schumi— Alex Stephenson (@TheAlexNews) December 31, 2013
His duels in his heyday with Hill and Jacques Villeneuve, fired by an unquenchable competitive spirit, have gone down in Formula One lore.
Schumacher was born in January 1969 near Cologne, Germany, the son of a bricklayer who also ran the local go-kart track, where his mother worked in the canteen.
By 1987, Schumacher was the German and European go-kart champion and was soon racing professionally. In 1991 he burst into Formula One by qualifying seventh in his debut race in Belgium and a year later, he won his first Formula One grand prix.
He joined Ferrari in 1996 and went from strength to strength over the next decade, dominating the podium, before retiring aged 37.
During his retirement he survived a horror accident that knocked him out when racing a motorbike in Spain, though that time he was released from hospital after just five hours.
But the father of two could not resist the lure of the track and in 2010 he came out of retirement, signing a deal with Mercedes before quitting for good in 2012.
His helmet had a message for fans: "Life is about passions -- Thank you for sharing mine."