Illness has robbed Richie Porte of an important pre-Tour de France hitout.
His BMC team announced on Thursday that Porte would not start stage two in the Tour of Romandie.
"Of course it's disappointing to have to stop, but I trust the medical team's advice that it's the right decision," Porte said in a BMC statement.
Team doctor Dario Spinelli said the Tasmanian had developed a fever and gastrointestinal problems the night before.
"(He) is not fit to start today, particularly given the difficulty of stage two," Dr Spinelli said.
"He is showing symptoms of a virus and hasn't had an appetite so it's not in his best interest to line up for a mountain stage with no fuel in the system."
Cold weather and snow have marred the start of the Swiss race, with almost 60km cut from the opening road stage.
Porte and American teammate Tejay van Garderen are among riders using the race as a key stepping stone to the July Tour.
They will be BMC's co-leaders at the Tour de France after Porte joined the team this season.
Their co-leadership plans raised eyebrows in the sport, but they showed it can work last month when Porte was fourth overall and van Garderen finished fifth at the Tour of Catalunya in Spain.
Porte is the only Australian with ambitions of a big general classification result at this year's Tour.
He also is a front runner to make the national road team for the Rio Olympics.