Rossi has Stoner in his MotoGP sights
However Stoner, 21, says he will not be forced into a change of strategy as the head-on battle continues in Sunday's German Grand Prix.
The race is the tenth round of an 18-event series with Stoner leading Rossi by 21 points after a whirlwind five victories from the opening nine races. Rossi has won three.
And despite the boost of his majestic win over Stoner in last weekend's Dutch TT, from 11th on the grid, Rossi is targeting Stoner and Ducati over the second half of the season.
"Casey is a great challenger for the title, he is fast, strong and is not making mistakes," the Italian said.
"He has the right package of bike and tyres and his Ducati is faster than my Yamaha in top speed. And when the track is wet, when the rain is strong, he is unbelievable.
"When you fight this kind of challenge you spend 100 per cent of your effort in every practice session, in every race."
The tight struggle between Rossi and the Aussie young gun is mirrored in the points. Over the past four races, since the Italian GP at Mugello, Stoner and Rossi have both scored 83 points.
But Stoner is not yet ready to contemplate lifting the world crown.
"I'll wait and see, now it's only halfway through the season, I'm just going to keep doing the best I can at every race," Stoner said.
"I'm taking the fight to Valentino this year so no matter what happens in the championship it is great to do that in the races, fair and square.
"I would just really like to see the points chase go down to the end of the season at least, and if Valentino wins the championship so be it.
"I haven't lost a point to him over the last four races, which means something, and Valentino has only beaten me three times out of nine races, with Chris Vermeulen winning the other race.
Yet to win a race is Spanish youngster Dani Pedrosa, 21, who was tipped by Rossi to be his main title challenger at the beginning of the season.
Pedrosa and Honda have struggled and he is now 64 points behind Stoner who has 185 points, Rossi 164 and Pedrosa 119.
Vermeulen is fifth on 88 with Honda's defending world champion Nicky Hayden out of contention after a poor season with 57 points.
Â© 2007 AAP
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