Roberts has been suffering all season with his arm "pumping up", causing pain and weakness during the races and spoiling his performance on the new four-stroke Suzuki GSV-R prototype. Now he is to have surgery to relieve the pressure, a common problem for motorcycle racers, and a common treatment.

Originally he had planned to have the operation during the summer break after next weekend's German GP. A deterioration in his condition over the past two races changed his and the team's minds, and they decide to go ahead directly to give him the longest possible time to recover.

"I've had problems ever since we started riding the four-stroke. The bike is heavier and takes more muscling around, and you also have to blip the throttle to back-shift while you're braking, which puts a lot more strain on your arm," explained a disappointed Roberts, after dropping from fourth at the start of the race to 14th.

"I've been suffering from fatigue and pumping up, and we planned to have the operation done quietly during the summer break.

"Then at the last round at Assen I had a lot more trouble than I'd anticipated. It's a very physical track, with no straight where you can rest even for a second.

"I had more trouble today, and after discussions with the team and the factory we decided it would be better to go ahead with the surgery directly. The usual recovery time is three to five weeks, but this will give us a little longer.

"I had to have it done anyway. The main thing is to get fit for when the season starts again in Czecho. We're expecting continued development for the bike there, so it is crucial for me to be at 100 per cent for that race."

Roberts will be replaced in Germany by Japan's Yukio Kagayama, the factory Suzuki racer who campaigns a GSV-R in the prototype class in the All-Japan Championship.