The former Formula One world champion Niki Lauda has expressed "disbelief " that Michael Schumacher is lying critically ill and in an induced coma in Grenoble after hitting his head on a rock in a skiing accident at the weekend.

Like Schumacher Lauda is a former Ferrari great who won two of his three titles while representing the Scuderia. He said: "I find it completely shocking and unexplainable why this great driver, who won seven championships in over 300 races and stayed alive, could have something like this happen to him. It's tragic.

"He was the greatest driver of them all, with seven titles. Only the great Juan Manuel Fangio comes close to him, with five. He was the perfect racer, with speed, instinct and a great technical understanding."

Lauda, who was involved in a near fatal crash as an F1 driver and is now non-executive chairman at Mercedes, added: "Michael is a very good skier and what happened to him could have happened to anyone. He's a perfect man, a solid man, an outstanding guy. He would not take unnecessary risks. He's not stupid. I certainly would not expect him to do something crazy in front of his own son."

Early in his career the skydiving, motorcycling, horse-riding and skiing Schumacher was described by Fangio as "the greatest of adventurers". Fangio said in the 1990s: "We racing drivers are adventurers. The more difficult something is, the greater the attraction that comes from it. Michael Schumacher is the greatest of the adventurers."

In 2009 the German suffered neck and spinal injuries in a serious motorcycling accident. And he is not the first F1 driver to find life more dangerous away from the track. Didier Pironi was killed in a power boating accident, Graham Hill died when the private plane he was piloting crashed and the rally champion Colin McRae was fatally wounded in a helicopter mishap.

In addition Mark Webber broke his leg on a mountain bike in Tasmania and Robert Kubica's highly promising F1 career ended when he crashed while taking part in a minor rally. Kimi Raikkonen, meanwhile, was injured in a snowmobile accident.

Lauda amitted he was very worried about Schumacher's condition. "The news is not encouraging at all. That is my worry and that is why I'm praying for him." Indeed the F1 world appears to be conducting a vigil at the bedside of the German, who is in a "critical situation" according to the chief anaesthetist Jean-François Payen.

One of his greatest rivals in the 1990s, Damon Hill, said: "We are all praying for Michael's speedy and full recovery and our thoughts are with Corinna [Schumacher's wife] and the children."

His fellow Sky F1 commentator Martin Brundle said: "Michael's accident is distressing and a great shock, and we have to be very concerned about his chances of survival and return to full health. From what we are told it looks very serious indeed, and we can only hope for the best along with his lovely family.

"Michael loves to challenge race tracks on superbikes and he often excitedly shows his many amazing skydiving pictures on his phone. He's only a year out of the F1 cockpit but as a driven and competitive person you can't simply switch off and settle down at the end of a long career.

"You need challenges and achievements to keep the adrenalin flowing. But from what I read he wasn't taking undue risks on the ski slopes, and it seems he's been very unlucky on this one. It's not uncommon for racers to survive many big accidents to then be injured in cars, aviation, bikes, on water, or indeed ski slopes. The need for machinery and speed will always be there, it's inevitable.

"When I read that Michael had received a blow to the right side of his head I couldn't help but think of Ayrton [Senna], and pondered why these things so often happen to the truly great."

The current world champion, Sebastian Vettel, who idolised Schumacher, said: "I am shocked and I hope that he gets better as quickly as possible. I wish his family much strength."

Derek Warwick, who raced in F1 in the 1980s and 1990s and is now president of the British Racing Drivers Club, said he believed Schumacher's fighting spirit would help him overcome his accident. "The world of motorsport is holding their breath at the moment. it is a very difficult time for everybody, It makes us realise how vulnerable we are," he said.

"People have to remember that racing drivers and bike riders are a different breed of people. They don't seek danger but we are people that live life to the maximum. I still do to this day and I am now 59 years old."

The German Chancellor, Angela Merkel, was "extremely shocked along with millions of Germans" to hear of Schumacher's plight. The government's spokesman Steffen Seibert said: "We listened to the doctors earlier as they described the situation as extraordinarily serious.

"We hope, along with Michael Schumacher and his family, that his injuries will heal and he will recover. We wish his wife, his children and the rest of his family strength and mutual support."