Michael Schumacher's family are doing "everything humanly possible to help him", they have said on the eve of his 50th birthday.
Schumacher, the most decorated star in Formula One history, has not been seen in public since he fell and hit his head in a skiing accident on the French Alps five years ago.
He is understood to be receiving medical care at the family home near Lake Geneva in Switzerland, but updates regarding his health have been few and far between.
In a statement published on Schumacher's official Facebook page, his family said: "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 if we are following Michael's wishes and keeping such a sensitive subject as health, as it has always been, in privacy.
"At the same time we say thank you very much for your friendship and wish you a healthy and happy year 2019."
The wall of secrecy, enforced at the request of the German's wife Corinna, was established to protect one of the biggest names in modern sporting times.
But the sporadic offerings about a driver who won a record seven world championships, 91 grands prix, and commanded a following of millions around the world, have led some to ponder whether more details should be made public.
However Ross Brawn, who helped mastermind Schumacher's success at Benetton and Ferrari and has visited the former champion in Switzerland, believes his family are right to conceal his medical condition.
"I am constantly in touch with Corinna, and I totally agree with their decision," he said.
"Michael has always been a very private person and that's been a guiding principle in his career, his life and his family always agreed with that choice.
"It's completely understandable that Corinna has wanted to maintain the same approach, even after the tragic event, and it's a decision we must all respect. I'm sure the millions of people who are still Michael fans will understand it, too."
Stephane Bozon, who was part of the rescue team in 2013, recently spoke about the incident.
He told German magazine FOCUS that the site of the accident made it difficult for first responders to transport Schumacher.
Mr Bozon also said he "saw the stone" that the German, who was skiing off-piste at the time, fell on to, splitting open his helmet.
"The special thing was that it had snowed so little in the days before that the stones were slightly covered with snow, but only with a very thin blanket of snow. He could not see the stone," Mr Bozon said.
"But if it had snowed more, Schumacher would probably just have glided over the first stone."
On Thursday, an Official Michael Schumacher App will be released allowing fans to view a "virtual museum" of his career.
His family said: "We are very happy to celebrate Michael's 50th birthday tomorrow together with you and thank you from the bottom of our hearts that we can do this together.
"As a gift to him, you and us, Keep Fighting Foundation has created a virtual museum. The Official Michael Schumacher App will be released tomorrow, so that we can review all together Michael's successes.
"The app is another milestone in our effort to do justice to him and you, his fans, by celebrating his accomplishments. We wish you a lot of fun with it."
Ferrari will also celebrate the great German's birthday by launching a special exhibition at their Maranello headquarters in northern Italy.
The display, which runs in association with the Keep Fighting Foundation - of which Brawn and FIA president Jean Todt are both trustees - will honour Schumacher's remarkable success with the Italian team.
Schumacher added to the two titles he won at Benetton with five triumphs for the Prancing Horse at the turn of the century.