The 2012 Giro d'Italia winner will now head home to try to fully understand and resolve the problems that have hampered him ever since last Saturday's time trial stage. He had slipped to 38th overall in the general classification, 32:55 behind race leader Vincenzo Nibali (Astana).
"It's heartbreaking," Hesjedal said in a statement from the team.
"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 TT. We're working on it, but we're not sure what's wrong."
"There's a virus that's been going around, so it could be that, or severe allergies, or going too deep on the TT combined with both – whatever it is, I'm only getting worse. Yesterday'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 last night, I also know that its time for me to go home, get some tests done and get healthy again."
"I have tried my best to honor the number one bib number, the race, my team and fans and it's devastating to leave this way. Going home now is heartbreaking. I'm very proud of the team – Ramunas' win proves that we all came here to race. These guys gave everything to help me. I couldn't ask for better teammates and I know that they'll continue to do great things here at the Giro for Garmin–Sharp. Now, I'll go home, focus on recovering and take things day by day, and I'll be cheering on the team from there."
Team physician, Shannon Sovndal explained: "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 so we decided it's time for him to go home, get testing done, and focus on getting healthy again."
Directeur sportif 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. He continued as long as he physically could because he wanted to honor the race and his team, but the health of our athletes is our priority and with that, we know its time for him to go home and focus on getting healthy again. The team here continues to be very motivated – we proved that on Stage 11 with Ramunas' win – and we will continue to fight for stage wins. There is plenty of racing still to be done and we know we will animate the rest of the race."
Friday's thirteenth stage is the longest in this year's Giro d'Italia at 254km and takes the riders across northern Italy from Busseto to Cherasco near Turin.