Renowned neurosurgeon Erich Riederer made the worrying claim in a new documentary for a French TV channel.
“He is breathing, his heart is beating, he can probably sit up and take baby steps with help, but no more.
“I think that’s the maximum for him. Is there any chance of seeing him like he was before his accident? I really don’t think so.”
The F1 legend’s health has been shrouded in secrecy since he suffered a near-fatal brain injury in 2013 after falling and cracking his head on a rock while skiing off-piste in the French Alps.
Since his accident in December 2013 there has been only scraps of information on his ongoing recovery.
By June 2014 he had regained consciousness and and left Grenoble Hospital for further rehabilitation for the University Hospital in Lausanne, Switzerland.
In September that year he left the Swiss hospital to continue his recovery at home.
Former Ferrari manager Jean Todt gave an interview in July 2019 saying that Schumacher was making “good progress” but also “struggles to communicate” but was able to watch Formula 1 races on TV.
Riederer’s claim comes just days after Schumacher’s ex-boss at Ferrari said he was “fighting” to recover.
Jean Todt, 74, is among just a handful of visitors allowed to see the 51-year-old – who is being cared for in Switzerland by his wife Corinna and their two children Gina-Marie and Mick.
Frenchman Todt oversaw five of Schumacher’s seven titles when he was team principal for Ferrari.
He said: “I saw Michael last week. He is fighting.
“My God, we know he had a terrible and unfortunate skiing accident which has caused him a lot of problems.
“But he has an amazing wife next to him, he has his kids, his nurses, and we can only wish him the best and to wish the family the best, too.
“All I can do is to be close to them until I am able to do something, and then I will do it.”
He said: “We must imagine a person very different from the one we remember on the track, with a very altered and deteriorated organic, muscular and skeletal structure.”
Acciari, who works for a hospital in Bologna, is not reported to have treated the sporting superstar.