And the chief doctor at a rehabilitation hospital in Basel, Switzerland, told Sonntagsblick newspaper: "The likelihood of a complete recovery for Schumacher is constantly lower.
"The famous, laughing, fast Schumi will probably not be seen again," coma specialist Mark Mader added.
"The longer someone is in a coma, the less well the brain can recover. When (Schumacher is) awake, severe damage is likely to remain."
Mader also defended those experts who have been speculating about Schumacher's condition and recovery, despite criticism.
"What is really the case with him, no one knows," he said. "Not even his medical team. The speculation is ultimately the prognosis."
According to Italy's La Gazzetta dello Sport, tests at the Grenoble hospital have shown that Schumacher, 45, is not paralysed.
But there are also rumours the great German, who weighed about 75kg at the time of his skiing crash in the French alps, has lost twenty kilograms in hospital.
Schumacher's last F1 teammate, Mercedes' Nico Rosberg, told an interview with Playboy magazine that reports of his countryman's condition are affecting him, as he knew the seven time world champion well.
"But I think that, if anyone can do it, it is Michael, with his will to fight," said Rosberg.