I agree with Lostboysaint. Although Rossi is being rather crude about it, it makes sense and he knows Stoner far better than any of us internauts.
Rossi has given his opinion, it is not some opinion he has conjured up to 'kick Stoner while he is down'. If you Stoner fans or people who are "over" Rossi don't like that you can go suck a bag of dicks.
I do too think Stoner's problems have more to do with the mind than his body.
You see, Stoner has only been able to win because of the Duke, he sets the traction control to a maximum and rings that bike around the track like the throttle was just a button. This of course requires a very special kind of talent because many other elite riders such as Hayden, Rossi, Edwards are not able to do this because they are "throttle-fearing" people.
Back in the day when TC wasn't invented, riders had to be ever so careful with throttle movement. Just 1 degree of movement equaled several horses and to open the throttle fully exiting a corner would spell an accident. It doesn't feel natural to open a throttle without a care with the knowledge that doing so could make you high-side...
Don't ask me to prove this, watch any race between '07 and now and you'll see Stoner opening throttle entirely far sooner than anyone else. And just hear the bike when you actually espectate a race, the engine is constantly changing revs unlike all the other engines which have a more smooth sound variation...
So knowing this, and the fact that the Duke is the most powerful bike on the grid, if you have a computer which is able to put the maximum power on corner exit pair that with a bloke capable of trusting this computer you have a great combination - Casey Stoner.
This is why Hayden hasn't been as good although with a great bike - he doesn't trust the computer. And don't tell me it's talent because Hayden has won a championship so he has the know-how.
I think that now that Stoner realizes this package no longer poses a greater competitive advantage which granted him his typical "run away lead" victories he is feeling the pressure, facing up to the fact that he can't do it any longer as in the past - now he has to fight "OLD SCHOOL STYLE".
Perhaps this coupled with the simple disappointment of losing is causing him some psychological stress. Although this is all speculation, I don't think these reasons are enough to make a fit young man mis out 3 entire races, or could it?
The body can cure quite quickly and definitely, being a high profile athlete grants you access to the best medical facilities so if he had anything they would have found it. Only things that doesn't cure quickly at a physical level might be serious diseases like cancer etc but something so serious would have been mentioned to the public.
What doesn't cure as fast as the body is the mind, 3 races of is what they're hoping his mind needs to recover.