John Degenkolb has been hospitalised for checks on his lungs and heart after having problems breathing and suffering a 'serious lack of power'.
In a statement issued by the German rider's Trek-Segafredo team on Friday, they said that the problems came to light during the Tour of Denmark last week. Degenkolb abandoned the race on stage five.
He had previously abandoned the Vuelta a España after four stages, suffering with bronchitis.
The team stressed that although Degenkolb feels well, he is staying in hospital as a precaution while the medical tests are being undertaken.
“In the last races he did, John suffered from breathing problems and a serious lack of power that prevented him to perform at his level," said Trek-Segafredo team doctor Jens Hinder.
"His condition was not improving enough over the last week, so we decided he had to undergo more profound examinations of his heart and lungs. John is feeling relatively well but has been hospitalised pending the results of these examinations.
"We will publish an update on his condition as soon as we have more information.”
Degenkolb's most successful season to date was in 2015, when he won both Paris-Roubaix and Milan-San Remo, going on to claim a stage of the Vuelta a España later in the year.
The following year, disaster struck. During a Giant-Alpecin training camp in January 2016, Degenkolb was one of six of the squad's riders hit by a car during a training ride. He suffered numerous cuts and bruises, and nearly lost one of his fingers due to a laceration.
The incident meant that he missed out on defending his Roubaix and San Remo titles, and only returned to racing in May 2016.
A switch from Giant-Alpecin to Trek-Segafredo followed in 2017. Although Degenkolb has only claimed one victory so far in 2017 – a stage of the Dubai Tour in February – he has performed solidly, with top 10 results in Paris-Roubaix, Tour of Flanders, Ghent-Wevelgem and Milan-San Remo.
Degenkolb had originally been on Germany's long list for the elite men's road race at the World Championships in Norway, taking place on Sunday, but withdrew his name due to illness.
