Armstrong completed the 185km opening stage in the peloton
Lance Armstrong's preparations for the Tour de France have suffered a setback after illness forced him to pull out of the four-day Circuit de la Sarthe race.
The seven-time Tour winner, who was 24th after the first stage, withdrew before Wednesday's 6.8km time trial.
His RadioShack team spokesman Philippe Maertens said: "Lance is not starting because of gastroenteritis."
Armstrong had indicated after stage one that six of his team's riders in France were struggling with a stomach bug.
The 38-year-old American, who was 27th in Sunday's one-day Tour of Flanders classic, managed to say on his twitter page: "Not so lucky I guess. Sicker than a dog now. This sucks."
Maertens added that Armstrong was suffering from diarrhoea, vomiting and a fever, and described his condition as "really bad".
Armstrong, who had already planned to miss the one-day Amstel Gold race in the Netherlands on 18 April, will head back to the United States as soon as he is able for recovery and to spend more time with his family.
Team sports director Alain Gallopin said "nothing has been decided" about his future race schedule.
"Maybe we will have to change his programme again. That's work for the coming days," said Gallopin.
"Lance was really keen on performing well, especially in the time trial of Wednesday afternoon.
"He showed his growing condition in the Tour of Flanders, where he came in with the first group sprinting for fifth place."
He plans to ride in the Tour of California in May and return to Europe for the Dauphine Libere or the Tour of Switzerland before the Tour de France begins on 3 July.
Meanwhile, Spanish rider Luis Leon Sanchez leads the Circuit de la Sarthe after winning a sprint finish into the town of Varades in the Pays de la Loire to take the mostly flat first stage in a time of four hours, nine minutes, five seconds.