Motor racing champion Michael Schumacher said on Tuesday he will not be able to make a temporary comeback. Tests had shown his neck couldn't stand the stresses of Formula One racing due to a severe neck injury he suffered in a motorbike accident in February.

Schumacher had delighted his fans and stunned the sporting world last month by agreeing to step in for Ferrari driver Felipe Massa,  who is recovering from an accident sustained in qualifying for the Hungarian Grand Prix on July 25.

"Yesterday evening, I had to inform Ferrari president Luca di Montezemolo and team principal Stefano Domenicali that unfortunately I'm not able to step in for Felipe," Schumacher said in a statement on his Web site.

"I really tried everything to make that temporary comeback possible. However, much to my regret it didn't work out."

He said test driving at Ferrari's own racetrack in Mugello, Italy, over the past two weeks and subsequent medical tests had shown his neck was still too weak for him to compete in F1.

"The consequences of the injuries caused by the bike accident in February, fractures in the area of head and neck, unfortunately have turned out to be still too severe. That is why my neck cannot stand the extreme stresses caused by Formula 1 yet," Schumacher said.