Casey crooker than Rookwood

What's wrong with Casey Stoner?

It was the question many were asking after the 2007 world MotoGP champion was finished exhausted and highly distressed at Assen last weekend - the second race in a row he was in this state - after a gutsy ride to third place.

A virus was blamed on his condition at the previous race in Barcelona.

Heading into Assen, Stoner pronounced he was good as gold and had resumed training without any issues.

But in the 45-min championship race in Holland, he faded quickly after an electric start, the debilitating physical condition that struck him down at Catalunya reappearing during the Assen race.

Afterwards, behind the podium, he was seen dry retching and close to collapse. He was excused from participating in the compulsory TV interviews and press conference.

"I've been feeling fine all week but started to feel run down again on Friday and I've just got worse as the weekend has gone on," Stoner admitted later.

"I've taken every kind of supplement and vitamin tablet you can think of but nothing seems to have worked, so it is obviously something we need to have looked at closer because I can't keep going like this and it is costing us points."

Ducati is very concerned about its young star's mystery ailment. There has been just eight days between the Assen race and the weekend's US GP at Laguna Seca, and Stoner can't afford to drop more points to his rivals, led by the rampant Valentino Rossi.

The Italian has certainly capitalised on Stoner's dramas at the last two races.

World champ Rossi goes into the US race in stunning from, with a five-point lead over Yamaha team-mate Jorge Lorenzo, with Stoner third in the standings.