The Olympic champion, Switzerland's Pascal Richard, has pulled out of the Giro d'Italia on medical advice. Richard is the key rider in the British team, Linda McCartney.
He and his team mate, Ben Brooks, were too ill to start Sunday's opening stage.
"Brooks was unwell when he started Saturday's time trial, and Richard became ill during the night," said team manager Sean Yates.
"They have a virus, with diarrhoea and flu symptoms. Our doctor, Roger Palfreyman, said it was best for them to pull out."
Sunday's opening stage was to have taken the riders on the 129 kilometre journey from Rome to Terracina.
Switzerland's Daniel Schnider and Niki Aebersold are still competing in the 3,700 kilometre marathon. But they are up against tough competition, including Paolo Salvoldelli, who is fresh from his victory in Switzerland's Tour de Romandie.
A Swiss victory is unlikely - the best the riders can hope for is to win some of the stages.
The Czech Republic's Jan Hruska, won Saturday's prologue race in Rome. He narrowly beat Paolo Salvoldelli to take the leader's pink jersey.
The race has been broken up into 21 stages and will take the 72 cyclists across Italy to finish up in Milan by June 4.
swissinfo with agencies