Schumacher's shunt happened at 198mph

Schumacher's spokesman he will need up to 12 weeks to recover.

The Williams driver spun and crashed heavily into a concrete wall during the US Grand Prix on 20 June, suffering concussion and back pains.

"Yesterday's diagnosis was a real blow," said Schumacher, who turned 29 on Wednesday, on his website.

F1 boss warns of death risk

"To be honest, I imagined my birthday would be rather different.

"But so be it. What's happened has happened. The injury is worse than feared. I have to get through it."

The discovery of the extent of his injuries means that Schumacher may not be fit to race again until latter stages of the season, which ends on 24 October in Brazil.

Spanish test driver Marc Gene will race for Williams at this weekend's French Grand Prix at Magny-Cours, where Schumacher won in 2003.

Team boss Frank Williams said: "I wish Ralf well for a full recovery, and I hope to see him back racing before the end of the season.

"In the meantime, we are fortunate to have a driver of Marc's calibre to fill the void."

Gene, a veteran of 34 GP starts, has raced at Magny-Cours twice previously, and has completed13,000km of testing in the FW26 so far this season.

"It is a shame that opportunities only come along when one of my colleagues has endured some kind of misadventure," he said.

"But it is my job to make the best of such circumstances and ensure the team is not compromised by Ralf's absence."