Former motor racing world champion Michael Schumacher is in a coma following a skiing accident in France - and doctors say they "cannot predict his future".
The 44-year-old German suffered a "serious brain trauma with coma on his arrival, which required an immediate neurosurgical operation," according to the hospital treating Schumacher in the French city of Grenoble.
Schumacher racing for Ferrari in his professional prime
At a press conference this morning, in Grenoble, doctors said he had suffered many lesions to his brain and his prognosis was unclear.
"He's in a critical situation - this is considered to be extremely serious," Chief Anaesthetist Jean-Francois Payen told journalists.
The doctor said that Schumacher's family were at his bedside and doctors were working "hour by hour" to help him.
"We are working day and night at his bedside," Dr Payen said. "It is too early to say anything as far as prognosis is concerned," he added.
Dr Payen said doctors had removed a clot to his brain and were now trying to reduce dangerous swelling.
Dr Payen added: "I'd say this accident happened in the right place because he was taken into hospital immediately and operated on as soon as he arrived, this meant his state is critical and he is still in a coma and he will be kept in a coma.
"Everything that needed to be done has been done at the moment we can't really say when he will recover, we cannot answer this yet."
The German Formula One legend skiing in Italy in 2006
Neurosurgeon Stephan Chabardes said an emergency brain scan had revealed internal bleeding, and injuries including contusions and lesions. He said they had operated a first time to treat the internal bleeding.
Dr Chabarde said: "I am very worried just like his family, we are very worried about his condition. The doctors won't tell you more because they can't tell you more, they are working hour by hour."
Sports journalist Gernot Bauer said four world-renowned doctors were looking after the driver.
Schumacher was wearing a helmet when he reportedly hit his head on a rock while skiing in the French Alps.
Doctors could not give a prognosis at a press conference in Grenoble
The press conference was told that without the helmet Schumacher would almost certainly have died.He was airlifted off the mountain following the accident in the resort of Meribel, in the popular Three Valleys area.
The sports star was skiing with his 14-year-old son and some friends when the accident occurred.
Schumacher's agent, Sabine Kehm, said: ''Michael fell on his head during a private ski trip in the French Alps.
"He was hospitalised and is receiving medical care. We ask for your understanding that we cannot give a running commentary on his state of health.
"He was wearing a helmet and was not alone.''
The accident occurred in the resort of Meribel in France
Journalist Carole Bouchard, from the French newspaper L'Equipe, said that the racing driver's condition had deteriorated during the hours following his hospitalisation.
The French Mountain Gendarmerie had earlier said Schumacher's life was not in danger.
Chris Chandler, a consultant neurosurgeon at King's College Hospital, said the immediate neurosurgical treatment given to Schumacher shows his injuries are severe.
"He could have suffered a diffuse injury to his brain which can then result in brain swelling," he said.
Schumacher made a comeback to Formula One for Mercedes in 2010
"He could have sustained some sort of brain haemorrhage and if there was a blood clot within his brain or on the surface of his brain underneath his skull, that might need to be removed.
"Sometimes there is nothing actually to remove but you put in an intra-cranial pressure monitor, which basically is an operation that requires drilling a hole in the skull and putting a fine probe inside."
Former Ferrari team boss Jean Todt and Professor Gerard Saillant, a brain and spine injury expert, are at the Grenoble University Hospital Centre where Schumacher is being treated.
Professor Saillant co-ordinated Schumacher's medical care after the driver broke his leg in the 1999 British Grand Prix.
Schumacher, a seven-time world champion, first retired from Formula One in 2006.
He has been hurt seriously once before, in a motorcycling accident in February 2009 when he suffered neck and spine injuries.
Schumacher recovered sufficiently from those injuries to make a comeback to Formula One in 2010.
Sports Broadcaster Derek Ryan says Michael Shumacher is a legend in formal 1: