The British Classics rider, twice a winner of Omloop Het Nieuwsblad, was diagnosed with the condition, which causes inflammation in the joints, last year. He has struggled with pain in his wrists, knees, and ankles, and has only raced once since the season resumed in August, abandoning the Tour de Pologne on stage 4.
"It’s disappointing to have to stop like this but it is clearly the right decision for my health and my family," Stannard said.
"We have explored all of the options this year to deal with my condition, and the team has been there with me every step of the way. I started to hope that I could manage the problem during lockdown, but as soon as I returned to racing I knew that my body wouldn’t be able to perform at any level anymore."
Ineos doctor Richard Usher explained: "We have tried various treatments but ultimately Ian has taken the best decision for his long term health."
Stannard started out on British Cycling's academy programme, cutting his teeth under the tutelage of Rod Ellingworth in a crop of talent that also included Mark Cavendish, Geraint Thomas, and Peter Kennaugh.
He was a stagiaire with T-Mobile in 2007 before turning pro with Landbouwkrediet-Tönissteiner and then riding for the ISD team in Italy and making his Giro d'Italia debut.
When Team Sky were set up in 2010, he was one of the riders on the first roster and has remained ever since, becoming one of their leading riders in the cobbled Classics.
Stannard won back-to-back editions of Omloop Het Nieuwsblad in 2014 and 2015, the latter famous for the way he overcame a numerical disadvantage in facing three QuickStep riders in a four-man finale. He also finished on the podium at the 2016 Paris-Roubaix.
"Growing up, the Classics captured my imagination. I always wanted to go over and race on the cobbles. Back in the first year of the Team, I finished third at Kuurne-Brussels-Kuurne in the worst conditions I’ve still ever raced in. Even now, our DS Servais Knaven still asks if I have dried out! I think there were only 26 finishers, and I’ve always thrived in those conditions," Stannard said.
"My favourite win was undoubtedly the second Omloop victory. I’d broken my back the year before, and the recovery process was the hardest I had to endure in my career. Then to beat three QuickStep riders, in Belgium… It doesn’t get much better really. People still ask me about that win all the time."
Stannard also wore the British national champion's jersey after winning the road race title in 2012, one of seven career victories that also include stages at the Tour of Britain, Herald Sun Tour, and Tour of Austria. He was also part of the teams that supported Chris Froome to Tour de France titles in 2013, 2015, and 2016, and to Vuelta a España titles in 2011 and 2017.
"I wanted to keep racing and that competitive fire still burns within me," he said. "But I am proud of what I have achieved in the sport and look back at my career with great pride, especially racing for this team. It’s been a dream come true.”
Ineos manager Dave Brailsford said: "Ian is a rider who gives so much to the race and his team mates and we all know that he always leaves it all out there on the road. He is one of the hardest, grittiest riders there is, whether racing hard on the cobbles of Belgium or pulling on the front at the Tour de France."
"He has been a core part of our team since day one and we will miss him, but he can look back proudly on a career that’s captured the true spirit of our sport and thrilled so many British cycling fans."
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