Schumacher was in a coma for six months after he banged his head on a rock despite wearing a helmet on December 29, 2013.
His current condition is not known as members of his inner circle state it is a private matter.
This month, his manager, Sabine Kehm, said: "Michael's health is not a public issue, so we will continue to make no comment in that regard."
"We have to protect his intimate sphere. Legally seen and in the longer term, every statement related to his health would diminish the extent of his intimate sphere."
But his former teammate Johnny Herbert has revealed the F1 legend has "good days and bad days".
And friend Ross Brawn said: "The family are conducting his convalescence in private and I need to respect that. So I don't want to comment on his condition beyond saying we're extremely hopeful we'll see Michael as we knew him at some point in the future."
Schumacher is believed to have been worth £500 million before the accident.