The British sprinter's team says the illness was caused by a bout of the Epstein-Barr virus.
Cavendish has won Scheldeprijs three times, while he was due to start just his third edition of Paris-Roubaix on Sunday.
Cavendish says he's confident with his early season form, and a stage 1 sprint victory in star-studded Abu Dhabi Tour backs that up.
The British sprinter avoids several crashes, including one in the final kilometer of racing.
Mark Cavendish manages to collect a podium finish in Dubai Tour stage 1 despite a flat tire.
A look at some of the awards we handed out at the conclusion of the 2016 season.
Cavendish looks for one more victory in Abu Dhabi at the end of a resurgent 2016 road season
The British rider will wear the leader's jersey during Saturday's stage 3.
Mark Cavendish rues a snap judgement in the worlds sprint finale. He bet Sagan would be boxed out, but ended up second-place.
Mark Cavendish finds himself momentarily stuck in traffic in a hectic sprint, possibly costing him a second world title