Casey Stoner's hopes of salvaging something from his Czech Republic Grand Prix weekend was ruined by a 'perfectly shaped' gravel stone that got caught in his Ducati's carboration.

The Australian was the leading the race at Brno when he slid off into the gravel trap, handing the lead to Valentino Rossi, who went on to take victory and extend his advantage over Stoner in the standings to 50 points.

However, Stoner believes he would have had the opportunity to get going again had a small piece of gravel, shaped exactly to that of the carboration, not got caught and prevent him from starting up again.

By restarting, it would have been possible for him to recover to second place and limit the damage to his fading title hopes.

"It was a perfectly-sized stone that got stuck in the carboration," the reigning champion told "You could search all the gravel traps in the world and you wouldn?t find one like it. We were just that unlucky."

Blaming a set up that had the bike leaning aggressively, Stoner is nonetheless confident Ducati have managed to get to the bottom of his problems.

"We made a big change which would have taken away the element of what caused the crash in the race. We've been leaning this bike over a long way, always scraping the footpegs. We took out that factor by changing the setup and the overall geometry.

"Now we can ride more on the bigger part of the tyre, which is safer and should give us more feedback. In any case, I'm a bit disappointed with the weekend but it is my only crash with a Ducati in a race. We've got to be pretty happy with how things have gone up to now."