Tour de France champion Chris Froome was forced to pull out of Sunday's Liege-Bastogne-Liege race at the last moment due to illness, Team Sky said.
Briton Froome has not raced since the end of March when he finished an underwhelming sixth in the Tour of Catalonia.
"Unfortunately Chris has been suffering from a mild chest infection," said Team Sky doctor Richard Freeman in a statement on the team's website.
"After an examination this morning (Sunday) we concluded that the best course of action would be to withdraw him from Liege-Bastogne-Liege as a precautionary measure, which will allow him the best chance of recovery ahead of the Tour de Romandie."
Froome was forced out of the Tirreno-Adriatico race in March due to a back problem before making his comeback in the Tour of Catalonia, where he was short of his best form.
The 28-year-old had started the season in fine form, winning the Tour of Oman in February for the second year in a row, but his season has since then been disrupted by injury and illness.
The Tour of Romandie, in which he is the reigning champion and which begins on Tuesday, is a crucial step in Froome's preparation for July's Tour de France defence.
AFter that he is due to race in the Criterium du Dauphine in June, where he is also the title-holder and which is considered one of the best gauge's of a rider's form before the Grand Boucle.
Briton Pete Kennaugh also pulled out of the Liege race, one of five 'Monuments' in cycling, due to an unrelated illness, Sky said.
Already Sky were due to begin the race a man short of their allowed eight-strong team, meaning there will only be five riders in the Sky ranks for Sunday's 100th edition of 'La Doyenne' (the oldest race) with Australian Richie Porte leading the way.