British road cycling star Mark Cavendish has been sidelined with a fatigue-inducing virus, his Team Dimension Data said Wednesday.
No date has been set for the return to the saddle of Cavendish, 31, who has not raced since the Milan-San Remo one-day event on March 18.
His absence was at first attributed to a cumulative right ankle injury.
But further tests have revealed that Cavendish, a 30-times Tour de France stage winner and one of the outstanding sprinters of his generation, is suffering from the Epstein-Barr virus
"Mark has been experiencing some unexplained fatigue during training," said Team Dimension Data doctor Jarrad van Zuydam in a statement.
"Unfortunately, there is no effective specific treatment against the virus but rest will be required to aid his recovery.
"It is difficult to give an accurate estimate of when we can expect him back at full fitness but we are hopeful of a significant improvement of his symptoms over the next two weeks."
Last year saw Cavendish win his first Olympic medal when, in his third Games, he took silver in the omnium at Rio as he combined his road career with a track programme.
Cavendish, from the Isle of Man off England's northwest coact, is just four wins away from equalling Tour de France great Eddy Merckx's record of 34 stage wins.
This year's tour starts in the German city of Dusseldorf on July 1 and Van Zuydam said: "His training load and symptoms will be monitored very carefully and he will make a gradual, step-wise return to full training and racing."
Meanwhile the team statement added: "(We) are in full support of the Manxman (a native of the Isle of Man) and his ability to bounce back from this unfortunate setback."