A few dozen fans assembled outside the Grenoble hospital where Michael Schumacher has been undergoing treatment since Sunday's accident in the resort town of Meribel, in which his head hit a rock when he fell while skiing off piste.
"For us Ferrari fans, we are just like brothers, we are just one," said one fan, Carlo Buschini, who raised his cap and blew kisses in the direction of Michael Schumacher's hospital room.
"We are here to celebrate and to celebrate his battle for life," said Buschini, speaking in Italian.
Supporters of the Scuderia Ferrari Club wore their team's red colours and carried a banner reading "Schumi, All our thoughts for you and your family."
In a blog post on its website, Ferrari said Michael Schumacher was "tackling the most important fight of his life" and sent him "double wishes" for his birthday.
Michael Schumacher is the most successful Formula One driver of all time with a record 91 race victories in a career spanning more than two decades. The German won five successive titles with Ferrari before retiring from the team at the end of 2006.
A less successful three-year comeback with Mercedes ended last year.
Messages of support appeared on Twitter from Michael Schumacher's former team mates.
"Happy Birthday my brother Michael! Be strong!! Be strong!! Don't give up!! We are praying for you," wrote Ferrari driver Felipe Massa.
Another former team mate, Rubens Barrichello, wrote "Keep it up, man ... I know ur (sic) fighting."
On Wednesday, Michael Schumacher's agent said he was in an artificial coma in stable condition, but no update has been given since then.