Doctors treating Michael Schumacher refused to predict the outcome for the former Formula One driver, saying they were taking his very critical head injury "hour by hour" following a skiing accident.
Chief anesthesiologist Jean-Francois Payen said the seven-time world champion was still in a medically induced coma. He said the medical team was focusing only on his current condition.
"We cannot predict the future for Michael Schumacher," Payen said. "He is in a critical state in terms of cerebral resuscitation. We are working hour by hour."
Schumacher, the most successful driver in Formula One history, arrived at Grenoble University Hospital Centre already in a coma and immediately underwent emergency brain surgery.
The German driver was skiing with his son on Sunday morning in the French Alpine resort of Meribel when he fell and hit the right side of his head on a rock. He was wearing a helmet, but the doctors said it was clearly not sufficient to prevent a serious brain injury. "Someone who had suffered this accident without a helmet would not have made it this far," Payen said.
Gerard Saillant, a trauma surgeon who operated on Schumacher when he broke his leg in a race crash in 1999, was at the hospital. He said he was there in his capacity as a friend, not a doctor. He did, however, say Schumacher's age - he turns 45 on Friday - and his fitness should work in his favour.
The Grenoble medical team, however, was being cautious about Schumacher's prognosis. They are working to relieve pressure on his brain and have lowered his body temperature to between 34 and 35 degrees Celsius as part of the medically induced coma.
The area in which Schumacher was skiing is part of a web of trails that slice down through a vast and, in parts, very steep snowfield.
Although challenging, the snowfield is not extreme skiing: the runs are broad and neatly tended, and the ungroomed area in between, known as off-piste, is free of trees.
Schumacher was conscious when first responders arrived on the scene, although agitated and in shock, according to the resort. He was airlifted to a local hospital and then later brought to the Grenoble facility.
His wife and other family members are by his bedside.
Schumacher has been seriously hurt before. He broke his leg in a crash at the Silverstone race course in 1999.
He also suffered serious neck and spine injuries after a motorcycling accident in February 2009 in Spain.
As news of the accident spread, Formula One drivers rushed to wish Schumacher a quick recovery.
Sebastian Vettel, who was once referred to as "Baby Schumi", said: "I am shocked and hope that he will get better as soon as possible."
Former Ferrari teammate Felipe Massa, who himself recovered from life-threatening head injuries at the Hungarian Grand Prix in 2009, wrote on Instagram: "I am praying for you my brother!! I hope you have a quick recovery!! God bless you Michael."
British former world champion Jenson Button posted that his "thoughts are with Michael Schumacher at this tough time. Michael more than anyone has the strength to pull through this".
During his career, Schumacher had seven drivers' championships and 91 race wins. After initial success with the Benetton team, Schumacher moved to Ferrari and helped turn the Italian team into the sport's dominant force.
After initially retiring in 2006, he made a comeback in 2010 and raced for three years with the Mercedes team.