The full, horrific extent of the neck and head injuries that prevented Michael Schumacher making a Formula One comeback have been revealed by his personal doctor.

Schumacher, who retired in 2006, had hoped to make a dramatic return to the track as replacement for injured Ferrari driver Felipe Massa in the European Grand Prix in Valencia.

But the 40-year-old winner of a record seven world titles was forced to abandon those plans following a special test session in a 2007 Ferrari Formula One 10 days ago.

At the time, the German merely said the lasting effects of damage to his neck sustained when he crashed a racing motorbike at 140mph in February meant he would not have been fit enough to last a Grand Prix.

But now Dr Johannes Peil has given a full list of the injuries Schumacher suffered when he fell from his Honda Superbike during a test session,

Dr Peil said: "He had a serious injury to the seventh vertebra of the neck, a fracture of the first left rib and a fracture at the base of the skull, roughly the size of a thumbnail but in a place supporting the whole weight of the skull.

"There was also a hairline fracture on the left side of the skull."

One of the two main arteries to Schumacher's brain was also damaged.

Incredibly, Peil claimed Schumacher could still race again. It is understood the injuries that stopped him racing on Sunday have healed well. Given more time for recovery, and special neck-strengthening exercises, Schumacher could return in 2010 if he wanted to.

Massa's car will now be driven by Italian veteran Luca Badoer at least until the Brazilian Grand Prix in October when Massa hopes to make his own comeback.

Meanwhile, Mark Webber believes that the championship has been thrown wide open after he and Red Bull team-mate Sebastian Vettel destroyed the aura of invincibility that had embraced Jenson Button.

Webber finished ahead of Button in the last three races, and third place last time out in Hungary means the Australian has narrowed the gap on the Brawn driver to 18.5 points. Vettel also beat Button at Silverstone, where the German sensation took the chequered flag, and at his home Grand Prix at the Nürburgring where he was runner-up to Webber. He retired his car in Hungary, but with 47 points to Button's 70 he is well within reach with seven rounds of the championship to go.

Webber said: "It looked like Jenson was going to win it. After six or seven races he and his Brawn GP team looked unbeatable. But we've proved that wrong in the last three races. We're still up there and we haven't been blown away by any means."

Button knows he faces a battle to hold off his Red Bull rivals and said: "With the cars at the front being so close at the moment it should be an interesting weekend."