Rory Sutherland has pulled out of the world road cycling championships in the United States and returned to Australia for personal reasons.
Sutherland posted on Instagram that he had to "abruptly" come back to Australia.
"We have been affected by a devastating and fast-moving cancer," he posted.
"I appreciate all the heart-warming support friends, colleagues and fans in this difficult time."
Sutherland also singled out Movistar, the Spanish professional team who employ him, for their support.
The 33-year-old has ridden as a domestique in the powerful Australian men's elite road team at the last two world championships.
Last year, teammate Simon Gerrans capped his career-best season by winning silver in the road race.
Luke Durbridge, who is already in Richmond, Virginia to ride the worlds team and individual time trials, will take Sutherland's place in the road race lineup.
Australia will again have several significant medal contenders in the worlds, which start on Sunday with the professional team time trials.
Rohan Dennis will be among the favourites on Wednesday in the men's time trial.
Rachel Neylan has returned to form ahead of the women's elite road race on Saturday, while Michael Matthews and Gerrans will lead the men's team for their road race on September 27.
This weekend's team time trials are the only events at the worlds based on professional, not national line-ups.
The Australian-based Orica-GreenEDGE men's team and their women's combination Orica-AIS have won medals every time since the event was introduced at the worlds in 2012.
But neither team has yet won the event.
Australian Orica-GreenEDGE rider Michael Hepburn was sick earlier this week, but it is understood he has recovered in time for Sunday's team race against the clock.