Classification leader Mathieu van der Poel and his team Alpecin-Fenix left the Tour of the United Arab Emirates on Monday.
A staff member of the Belgian team has tested positive for the corona virus.
"We have withdrawn to keep the bubble safe and to keep the course going," Alpecin-Fenix said in a statement.
"All team members will continue to be tested in the coming days while they are in quarantine."
The news is a setback for Van der Poel, who had started the first WorldTour race of the year on Sunday by winning the first stage.
He automatically took the leader's jersey.
The loss of the Dutch champion in the UAE Tour means that David Dekker is the new leader in the standings.
The talented sprinter from Jumbo-Visma had finished second in the opening stage.
Van der Poel registers with a mighty sprint victory in the first road race
Van der Poel is facing an important year
The race in the Emirates was for 26-year-old Van der Poel as the start of his preparation for an important cycling year, in which he is aiming for participation in the Tour de France and an Olympic title on the mountain bike after the spring.
Last year, the corona virus also played a major role in the Tour of the UAE.
At the time, the COVID-19 outbreak meant that the last two stages were canceled and that some teams were stuck in a hotel for more than a week.
The current edition of the Tour of the UAE will last until Friday.
On Monday the riders will complete an individual time trial over 13 kilometers.