[Read: Germany vow to win World Cup for Michael Schumacher]
Schumacher, 45, was transferred from Grenoble University Hospital in France where he had been in coma after suffering brain injuries in an skiing accident in the French Alps last December. Schumacher was taken to a rehabilitation centre in Lausanne.
It was said that Schumacher was no longer in the artificial coma and would undergo rehabilitation soon but Dr Riederer had a world of caution even though he praised Schumacher's progress in waking from a coma after six months.
Schumacher will struggle to form even a sentence, said Dr Riederer
The neurologist, who has an extensive experience in dealing with coma patients, said that Schumacher would remain invalid for the rest of his life and would need others' help, reports quoted him as saying.
Schumacher, who is said to have lost weight alarmingly during this time, is unlikely to recover fully, the doctor said, adding that it will be a success for Schumacher even if he manages to sit unaided within three months. Dr Riederer also told that Schumacher would find it difficult even to form a sentence.
Schumacher's former doctor Gary Hartstein had also warned earlier that the former F1 champion could be in a "minimally conscious state".