Rossi worried about Stoner's speed

After a dip in form in the early part of the season, the MotoGP world champion bounced back with a dominant win in the British Grand Prix at Donington last weekend.

Stoner followed it up by blitzing the field in opening practice for the Dutch TT at Assen.

And Rossi believes that such a performance indicates Ducati have turned the corner in their development of the GP8.

"It is not just two tenths [Stoner is ahead], it is seven I think, so more than half a second," he said on Thursday. "It looks like Ducati are able to use something that before was not ready.

"I think in the engine department or the electronics to open the throttle.

"Casey has riden very fast and on the limit all season, but now he is one second faster, so they must have found something different that is very strong to use."

Rossi urged Yamaha to pull out all the stops and speed up development of their own engine software in an effort to match the Ducati for pace. But he added that he feared it would be difficult to do this before MotoGP's month-long summer break, which begins after Laguna Seca on July 20.

"We are already working in the same direction to make for better acceleration, but it is not ready yet and we are waiting for new software as soon as possible," he said.

"Now with the performance of Stoner I think we try to force it through faster. But I don't know if it is possible before the break.

"Also maybe you need to test it and have one full day, and now the next test is in Brno. We try to force the time from an improvement point of view and we hope it is ready as soon as possible."