Former Formula 1 driver Michael Schumacher could be in coma for the rest of his life, according to reports in Germany.

The Daily Mail reports that German publications Focus and Bild have claimed that the 45-year-old's situation is so grave that he may not be woken up by the doctors treating him.

The former seven-time F1 world champion has been in an induced state of unconsciousness for the past 18 days in hospital in Grenoble, France after suffering brain injury during a low-speed ski accident on December 29.

Schumacher was initially said to be in a critical condition, but he has improved over the last two weeks or so, although there are suggestions that he may be kept in a coma for the rest of his life.

"We should not speculate here," neurosurgeon Andreas Zieger of the University Clinic for Neurosurgery in Oldenburg told Focus magazine.

"Ultimately, we are talking about life and death. A coma can in theory be maintained for a lifetime. It won't hurt the human brain."

"Brain injuries are among the most complicated injuries that can happen to the human body. Predictions about how long a person might be in a coma or potential complications are seldom reliable."

Cologne neurological expert Professor Gereon Fink believes that Schumacher being in coma for over two weeks means that he has suffered significant brain damage.

"If the injuries are so severe that it would harm the patient, he is kept longer in the medically-induced coma," he said.

"Depending on where bleeding has taken place can lead to unilateral paralysis, speech disorders or personality changes."

Schumacher has undergone two operations since the accident at the resort of Meribel last month.