GRENOBLE, France -- Doctors treating Michael Schumacher refused Monday to predict an outcome for the seven-time Formula One champion, saying they were taking his critical head injury "hour by hour" following a skiing accident.
Schumacher remained in critical condition after undergoing brain surgery following a skiing accident in the French Alps a day earlier, the doctors said.
The Grenoble University Hospital Center said the retired racing driver arrived at the clinic in a coma and underwent immediate surgery for a serious head trauma.
In a news conference held Monday morning, chief anesthesiologist Jean-Francois Payen said Schumacher was "fighting for his life."
"We judge him to be in a very serious situation," Payen said, according to a BBC translation. "We cannot tell what the outcome will be yet. We are working hour by hour, but it's too early to say what is going to happen and to have a prognosis.
"We think his helmet did help; without a helmet he wouldn't be here now."
Payen, who is also in charge of Grenoble University Hospital's intensive-care unit, said doctors couldn't "predict the future" for Schumacher.
"He is in a critical state in terms of cerebral resuscitation," Payen added, according to The Associated Press. "We are working hour by hour."
Payen said Schumacher was being kept in an artificial coma and a lowered temperature while doctors work to supply oxygen to the brain and reduce outside stimuli. When pressed, he said that they could go no further than his current status.
Schumacher fell while skiing in Meribel earlier Sunday and hit his head on a rock, according to a statement from the resort. Schumacher's 14-year-old son was skiing with his father when the accident happened, the resort said.
Resort managers said he was conscious when rescuers first responded to the scene though agitated and in a state of shock.
But Payen said Monday that after the fall Schumacher was not in a "normal state of consciousness." He was not responding to questions and his limbs appeared to be moving involuntarily.
He was airlifted to a local hospital and then later brought to Grenoble. Doctors said that stopover was typical and did not affect his condition.
His wife and other family members were by his bedside.
"The family is not doing very well, obviously. They are shocked," said his manager Sabine Kehm, who added that the family still appreciated the outpouring of support.
The French prosecutor in Albertville has opened an investigation into the accident, according to the Mountain Gendarmerie in Bourg-Saint-Maurice, which will participate in the probe. The goal is to determine the circumstances of the accident and what was responsible for it.
Earlier in the day, the Meribel resort said Schumacher had been taken to Grenoble for tests and authorities said his life was not in danger.
But the situation began to appear more serious when the resort said that orthopedic and trauma surgeon Gerard Saillant had traveled from Paris to the hospital in Grenoble. German news agency dpa said it was Saillant who operated on Schumacher when he broke his leg during a crash at the Silverstone race course in 1999.
But Saillant said he was there in his capacity as a friend, not a doctor. He did, however, tell reporters that Schumacher's age -- he turns 45 on Jan. 3 -- and his fitness should work in his favor.
The Grenoble medical team was being very cautious about Schumacher's prognosis. They are working to relieve pressure on his brain and have lowered his body temperature to between 93.2 to 95 degrees as part of the medically induced coma.
The neurology team at Grenoble is recognized as among the best in France and the hospital, in a city that is the gateway to the French Alps, sees a large number of skiing accidents every year.
The area where 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 -- where the resort said Schumacher was found -- is free of trees.
As news of the accident spread, Ferrari, which Schumacher raced for, expressed its concern in a statement.
"Everyone at Ferrari has been in a state of anxiety since hearing about Michael Schumacher's accident," it said, adding that company president, Luca di Montezemolo, and race team leader, Stefano Domenicali, were in contact with the family.
Many Formula One drivers used social media to wish Schumacher a quick recovery.
His former Ferrari teammate Felipe Massa, who recovered from life-threatening injuries sustained 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."
Support also came from leading German sports personalities, ranging from the NBA to soccer.
Boris Becker, the retired tennis champion now working with Novak Djokovic, posted:
Let us all pray for @realschumacher michael for a full and speedy recovery !!!— Boris Becker (@TheBorisBecker) December 30, 2013
An earlier tweet used in this story came from an unverified Sebastian Vettel Twitter account and has been removed. Vettel is a four-time F1 champion who is close to Schumacher.
In addition to the crash at Silverstone, Schumacher was hurt seriously in a motorcycling accident in February 2009 in Spain when he suffered neck and spine injuries.
Those injuries prevented him making a comeback that year to stand in for the injured Massa, however he came back to the sport full time in 2010.
Schumacher is the most successful driver in Formula One history, with seven drivers' championships and 91 race wins.
After initial success with the Benetton team, he moved to Ferrari and helped turn the Italian team into the sport's dominant force. After retiring in 2006, he made a comeback in 2010 and raced for three years with Mercedes.
Information from The Associated Press was used in this report.