Givrins, Switzerland - Former Formula One world champion Michael Schumacher has called off a planned start this weekend in the German superbike series, saying he was still feeling the effects of a crash two months ago.

The record seven-time F1 champion was due to compete in the first race of the German IDM series at the Lausitzring in eastern Germany.

"Unfortunately I have had to call it off because I am not yet ready," he told German Press Agency dpa in Givrins, Switzerland.

Schumacher said he was still feeling the knocks after crashing during a test drive at Cartagena, Spain on February 11.

"At the moment I can just about manage to ride a bicycle. When I have to move my neck quickly I am restricted," he said.

Schumacher had spent the winter training for the championship after taking part in the series on a few occasions last year.

The 40-year-old German, who retired from Formula One at the end of 2006 after 91 Grand Prix victories, said the crash at Cartagena had shown he was riding at his limit on the wrong track.

The German was testing a Honda 1000 CBR-Fireblade at the track when the accident took place. He was taken to hospital but a scan ruled out serious injury.

He said he would be choosing his racing carefully during the season, leaving out circuits which he considered too dangerous for his ability.

"Motorbike riding is a fun thing. Of course, I will be taking it as seriously as possible but with the knowledge in the back of my mind that I can't be first any more," he said.

"I want to do the things that I enjoy but don't have any hidden hopes."

Schumacher said motorbike and Formula One racing were two entirely different sports.

"The emotions and driving feeling are much more intensive than in a racing car, you are so close to the ground," he said of bike racing.

"The sensitivity you need on a motorbike is enormous. In addition the learning process is so interesting. Together with the emotions which are released it is a thing that gives me a great deal of fun."

However, you did not have to be as fit as in Formula One, he added.

"Last year I didn't really prepare and train. However I did realize I had a few deficits. Then I got ready this winter but unfortunately the accident got in the way." (dpa)