Bradley Wiggins (Team Sky) has withdrawn from the Giro d’Italia ahead of stage 13 on medical grounds.
The Tour de France champion, who had dropped to 13th overall, more than five minutes behind race leader Vincenzo Nibali (Astana), is suffering from a chest infection and will return to the UK for treatment.
Team Sky will now ride in support of stage ten winner Rigoberto Uran, who is third in the general classification, two minutes and four seconds adrift of the maglia rosa.
Team principal Dave Brailsford said: “We monitored Bradley overnight and this morning we’ve withdrawn him from the Giro after consulting the team doctor. His chest infection has been getting worse and our primary concern is always the health of our riders.
“Bradley will return to the UK today for treatment and to rest and we hope to have him back on the road as soon as possible.
“As a passionate racer he wanted to continue but he is simply unable to do so on medical grounds.”
Wiggins went into the race as favourite, bidding to add a second Grand Tour to his palmares having become the first Briton to win the Tour de France last July.
But the 33-year-old endured a difficult first week, crashing on a wet descent on stage seven to concede more than a minute to his rivals for the title, before failing to win back the deficit in his specialist event, the individual time trial, on stage eight.
Wiggins lost more time on stage ten, the first high mountains summit finish of the race, and, with his chest infection worsening, was dropped from the peloton on stage 12, on which Mark Cavendish (Omega Pharma-QuickStep) recorded his 100th professional victory.
“Brad developed a head cold and a chest infection and has been on antibiotics,” said Brailsford after stage 12. “His illness has got progressively worse and we knew ahead of the race this morning it was going to be tough for him to get through the stage.
“When you see a rider of Bradley Wiggins’s calibre struggling to hold the wheel in front of him on the flat, you know that he is ill.
“When you are ill, you are ill and all you can do is your best to try and manage that illness. I think he showed great courage to battle through the stage to the finish.”
Meanwhile, defending champion Ryder Hesjedal (Garmin-Sharp) has also quit the race.
The Canadian lost more than 20 minutes on the first mountain stage and, after continuing to struggle on stages 11 and 12, had slipped to 38th overall, 32 minutes and 55 seconds adrift of Nibali.
“The conditions on Thursday’s rainy, cold stage combined with Hesjedal’s deteriorating physical condition proved too much,” Hesjedal’s team said in a statement.
Hesjedal added: “It’s heartbreaking. I built my entire season around the Giro and I came here feeling great, but I have been suffering since the time trial.”