Defending champion Ryder Hesjedal of Boulder-based Team Garmin-Sharp has withdrawn from the Giro d'Italia, the team announced early Friday.
Hesjedal, the first Canadian to win a Grand Tour race, was in 38th place, 32:55 behind Italian leader Vincenzo Nibali of Team Astana.
"It's heartbreaking," Hesjedal said in a statement. "I want to be here for my team and for all the people who have supported me to get me here to this point.
"I built my entire season around the Giro and I came here feeling great, but I have been suffering since the (time trial). We're working on it, but we're not sure what's wrong."
Hesjedal's troubles began at Saturday's time trial when he finished 18th, 2:23 behind. He again suffered on Sunday's Stage 9 and the rest day Monday did little help. He then struggled on the first climb of Tuesday's Stage 10 and after the team's medical staff evaluated him that night he suffered again Wednesday while teammate Ramunas Navardauskas won in windy, rainy conditions.
Hesjedal lost another 1:16 on Thursday's Stage 12. He did not start Friday.
"There's a virus that's been going around, so it could be that, or severe allergies, or going too deep on the TT (time trial) combined with both — whatever it is, I'm only getting worse," Hesjedal said. "(Wednesday's) stage was just too much for me. I fought to get through it, and I know everyone suffered. But after seeing the medical staff, I also know that it's time for me to go home, get some tests done and get healthy again."
Britain's Bradley Wiggins, one of the co-favorites along with Nibali and Hesjedal, also withdrew after suffering from an illness.
Said Garmin-Sharp physician Shannon Sovndal: "The athlete's health is our priority. We've been trying to uncover what's going on with Ryder. He came into the race in stellar form, ready to defend his title, and clearly he's been suffering since the TT. His condition is not improving."
Team director Charly Wegelius added: "Ryder is an incredible champion and a phenomenal athlete. It's difficult to see him struggle this way as he came here in outstanding form — he built his season around the Giro."
Entering Friday's relatively flat 152.4-mile Stage 13 from Busseto to Cherasco, Boulder's Tom Danielson is Garmin-Sharp's leading rider in 40th place, 37:28 behind Nibali. Boulder's Taylor Phinney of Team BMC Racing is 159th, 1:56:38 behind.