Milan - Giro d'Italia contender Fabio Aru's pre-race build-up suffered a blow Sunday when he was forced out of Tirreno-Adriatico with a bout of bronchitis.
Aru is one of several contenders for the three-week Italian epic in what is its centenary edition, alongside former champions Vincenzo Nibali and Nairo Quintana.
But his team Astana announced: "Unfortunately, Fabio Aru has suffered, even in the night, of a tracheobronchial acute bronchitis, with fever.
"Therefore, in accordance with management and medical staff of the Astana Pro Team, it was decided not to start the fifth stage of Tirreno-Adriatico today to allow him to recover from the illness."
Tirreno-Adriatico was only one of two stage races Aru had targeted as part of his Giro preparations along with next month's Tour of the Alps.
The illness caused him to lose nearly five minutes to Quintana on Saturday, when the Colombian raced to victory on the summit of stage four.
Although climbing specialist Quintana will be a big focus as he attempts the first part of a Giro-Tour de France double this summer, the rivalry between Aru and Nibali threatens to steal the spotlight.
Aru was Nibali's trusted teammate when the latter won a dramatic 2013 edition, after racing through a snow blizzard on the Tre Cime di Lavaredo climb in the Dolomites to secure overall victory.
Nibali, the 2014 Tour de France champion who also won the Tour of Spain in 2010, now races for the Bahrain team. Aru has moved up to become the team leader at Astana.
The pair have largely avoided each other in Grand Tours since 2013, meaning the 2017 Giro d'Italia sets the scene for a potentially epic battle for the pink jersey.
Organisers went to great lengths to make sure both compete at the May 5-28 race.
The 100th edition starts on Aru's native island of Sardinia, taking in three stages before crossing over to Nibali's home island of Sicily for stages four and five.
Aru is now set to attend a training camp in Sierra Nevada and line up in the Tour of the Alps on April 17-21.