Mark Cavendish has withdrawn from the Driedaagse De Panne in Belgium because of a viral infection.
The Omega Pharma - Quick-Step rider also pulled out of Sunday's Gent-Wevelgem race with the illness.
The Manxman, 28, has returned home and will undergo tests ahead of Sunday's Tour of Flanders.
"I started vomiting and having diarrhoea again last night," he said on Tuesday. "I'm in no shape to start because I can't eat or drink anything."
The Driedaagse De Panne is a three-day stage race ahead of the Tour of Flanders, which is the third of seven one-day 'Spring Classic' races.
Cavendish finished fifth in the Milan-San Remo race on Sunday 23 March, but began feeling ill the following Wednesday and pulled out of the Gent-Wevelgem on Friday.
The Gent-Wevelgem race was won by German rider John Degenkolb, who beat Frenchman Arnaud Demare and the defending champion, Peter Sagan of Slovakia, in a bunch sprint finish.