Marlboro Ducati's Casey Stoner is staying on in American to undergo extensive medical tests in an attempt to disgnose the cause of the physical exhaustion which hits him mid-race.

The Australian former champion is to see the legendary Dr Ting at his California centre to try and solve the problem which saw Stoner in a daze at the end of the Laguna Seca MotoGP 32-lapper.

“It has been a weekend to forget. I can’t be happy with fourth place even if it has limited the damage to my championship chances. Today I didn’t feel as bad at the end of the race as I have done in the last two but I’m still not right. I found it really difficult to keep my concentration over the last few laps and I was in a bit of a daze by the end," said Stoner.

"My left arm was feeling really tired by the end because of the fact there are so many left-handers here and my left wrist still doesn’t have the full range of movement after my operation in the winter. I’m really disappointed because without all of these problems we could have done so much better.

"I want to thank the team for giving me a great bike and also Doctor Claudio Macchiagodena and our physiotherapist Freddie (Dente) for all their help. Now we’ll focus on trying to find out the root of the problem because racing in this condition is not much fun.”