Stuttgart - Michael Schumacher's manager Willi Weber has revealed the seriousness of the motorbike accident that has put an end to the German's plans for a Formula One comeback.

"It was the most serious accident in Michael's motorsport career," Weber told German Press Agency Tuesday.

The seven-time world champion was set for a sensational return in place of injured Ferrari driver Felipe Massa for several races, starting with the European Grand Prix on August 23, in Valencia, Spain.

However, the 40-year-old revealed that the fractures sustained in the area of the head and neck in the bike accident last February in Spain meant that his neck could not stand the extreme stresses caused by Formula One.

"It's a real pity. Like everyone else, I was really looking forward to the comeback," said Weber.

Schumacher's most serious accident in F1 came at Silverstone in 1999 when he suffered a broken leg after his Ferrari ploughed into a tyre wall. (dpa)