Schumacher, who retired from the sport for a second time in 2012, fell while skiing off-piste with his son at the Meribel resort and hit his head on a rock.
The 44-year-old German was transported by helicopter to a hospital in Moutiers before being transferred to a clinic in Grenoble.
"He had some lesions in his brain when he came in" and we "had to operate him urgently to release some pressure," one of the doctors treating him in Grenoble told a press conference.
Schumacher was wearing a helmet at the time but nevertheless suffered injuries to the right side of his brain.
"He's in a critical situation and we can say that he's fighting for his life," said anaesthesiologist Jean-Francois Payen, one of the doctors in Grenoble.
"We judge him to be in a very serious situation. We can't tell you what the outcome will be yet."
Doctors treating said they were taking his very critical head injury "hour by hour". Prof Payen told reporters that the medical team was focusing only on his current condition.
"We cannot predict the future for Michael Schumacher," Payen said. "It's too soon to talk about."
Schumacher remains in critical condition with severe bruising on his brain, the doctor said.
On Sunday morning, the German driver was skiing with his son when he fell and hit his head on a rock. He was wearing a helmet at the time, 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.
Doctors contradicted earlier French media reports that Schumacher had undergone a second operation overnight.
Payen ruled out further surgery for now,saying "at this moment we don't think he'll need a second operation".
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, 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 first airlifted to a local hospital and then later brought to Grenoble for more extensive treatment.
His wife and other family members are by his bedside. ESPN F1 also reported that Jean Todt, his former Ferrari team boss and now president of motorsport's governing body, the FIA, was at the hospital.
Schumacher has been seriously hurt before. He broke his leg in a crash at 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.Sebatian Vettel, who was once referred to as "Baby Schumi", told German news agency dpa: "I am shocked and hope that he will get better as soon as possible."
His former Ferrari teammate Felipe Massa, who himself recovered from life-threatening head 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."
British former world champion Jenson Button said 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 Mercedes.