Adding that his friend's difficulty with communicating has saddened him.
"His family is fighting just as much and of course our friendship cannot be the same as it once was.
"Just because there's no longer the same communication as before.
"He continues to fight. And his family is fighting the same way."
The intensely private Schumacher family have given out few details about the F1 legend’s health over the years.
Not much is known about his recovery, other than that he received rehabilitation treatment at the University of Lausanne before being moved to his home in Switzerland, where he currently remains.
A rare statement was released in January, saying: “We are doing everything humanly possible to help him”.
“You can be sure that he is in the very best of hands and that we are doing everything humanly possible to help him.
“Please understand we are following Michael’s wishes and keeping such a sensitive subject as health, in privacy.
“At the same time, we say thank you very much for your friendship and wish you a healthy and happy 2019,” the statement said.
Schumacher remains the only driver in history to win seven Formula 1 World Championships, five of which he won consecutively.
He is still the most successful driver in the history of the sport.