"Quite a few people have suggested I might have Epstein-Barr or something, and I've had some doctors say no way," said Stoner. "I've read that everyone has Epstein-Barr and if you don't have enough rest, you get it. I've been traveling and racing and working out for years. But, it's not the only possibility out there.

"If it is Epstein-Barr and rest is the only help, then I'll get rested up during the long off season. I might have to back off in my training, traveling or something. But first, we need a diagnosis, and then take it from there."

Stoner is now 16 points behind Rossi and seven from Lorenzo after eight of the 17 rounds.

Round nine of the MotoGP World Championship takes place at the Sachsenring in Germany on July 19, with the British Grand Prix - the final event before the summer break - just one week after.

Additional reporting by Lynne Huntting.