Cadel Evans is considering cutting short his disappointing 2012 season because of illness.
The 2011 Tour de France champion has endured a rough time with his health this year and his team, BMC, reported he was suffering a "suspected low grade infection".
BMC doctor Max Testa said the illness could be enough to stop him competing at next month's world titles in the Netherlands.
"Despite his usual full commitment and attention to training, Cadel has been experiencing unusual ups and downs on his performance," Testa said.
"Getting him back to full health and to his physiological standard of performance is a priority for the BMC Racing Team.
"If the testing goes as expected, Evans may return for the Grand Prix Cycliste de Montreal on September 9 in Canada."
Evans has had a tough couple of months, finishing seventh at the Tour de France before pulling out of the time trial at the London 2012 Olympic Games.
"I didn't know what was holding me down at the time," Evans said.
"Now we have a better idea, and it's a relief to have some indicators as to why I have been under-performing.
"When you don't know why you're not performing, you have to ask a lot of questions of yourself."