MotoGP world champion Casey Stoner suffered a hard fall from his Repsol Honda in the opening minutes of Friday's final practice at Assen.

The Australia highsided at the Turn Nine left-hander due to a sudden rain shower. Rain flags were raised by marshals just as Stoner tipped into the corner and several other riders ran straight on just behind him.

Stoner, who was on his third lap, was slow to walk away following the heavy fall, but eventually returned to the pits on the back of a scooter and appears sore but unharmed.

The rain has now stopped but all riders are still in the pits with 30 of the 45-minutes remaining.

Stoner, who starts this weekend 25 points behind Jorge Lorenzo in the championship, also fell heavily in Friday practice at Assen last year. Lorenzo was fastest at the time of this morning's rain.