Doctors treating Michael Schumacher have refused to predict an outcome for the Formula One great, who is fighting for his life after a skiing accident in the French Alps.
Jean-Francois Payen, the anaesthetician at the CHU hospital in the eastern French city of Grenoble, said on Monday that Schumacher was still in a medically induced coma with head injuries, sustained when he fell while skiing with his 14-year-old son at the Meribel resort on Sunday.
"We can say that his condition is life-threatening," Payen said.
"For the moment we cannot say what Michael Schumacher's future is.
"He is in a critical state in terms of cerebral resuscitation."
Payen said that the medical team was working around the clock and were trying to win time in the their fight to save the seven-time Grand Prix champion.
The 44-year-old German had slammed his head on a rock while skiing off-piste in the French Alpine resort where he has a vacation home.
Payen said Schumacher would have died without the helmet.
Philippe Quincy, the Albertville public prosecutor, told Reuters news agency that an inquiry had been launched on Sunday to identify the causes of the accident.
Initial findings indicated the blow was so hard that Schumacher's helmet had shattered.
"We know that the accident took place in an off-piste zone where rocks were partly or totally hidden by snow," Quincy said.
Schumacher was initially conscious as he was transported to a local hospital in Moutiers and then to Grenoble. However, his condition deteriorated sharply afterwards.
Neurosurgeon Stephan Chabardes said an emergency brain scan carried out on Schumacher had revealed internal bleeding and injuries including contusions and lesions. He said they had operated to treat the internal bleeding.
Doctors said Schumacher had been placed in an artificial coma but, contrary to an earlier French media report, said they had not carried out a second operation during the night and were not planning any further interventions at this stage.
The neurology team at Grenoble University Hospital, which is recognised as among the best in France, was cautious about Schumacher's prognosis.
They lowered his body temperature to between 34 and 35 degrees Celsius as part of the medically induced coma, which
essentially rests the brain, slowing its metabolism to help reduce inflammation after an injury.
German Chancellor Angela Merkel joined sports legends and millions of Germans on Monday in expressing shock at Schumacher's skiing accident, as his family thanked well-wishers for their support.
F1 world champion Sebastian Vettel wished Schumacher's family strength, as they kept a vigil by his hospital bedside.
"I am shocked and I hope that he will get better as quickly as possible," Vettel said.
Felipe Massa, former Ferrari team mate, wrote on Twitter: "I'm praying for God to protect you, brother!", while double F1 world champion Fernando Alonso tweeted: "Get well soon Michael! Hope to hear some positive news very soon! #strongman".