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Spanish Tour de France champion Contador blamed contaminated meat for the breathing drug clenbuterol, which in a performance-enhancing context builds muscle mass and burns fat, found in his urine sample in 2010.
Mexico middleweight Saul "Canelo" Alvarez, one of the biggest names in boxing, also claimed the red meat excuse after he failed a voluntary test for the same drug ahead of his rematch with Gennady Golovkin in 2018.
The Fury's case has now taken an explosive turn with Carefoot saying he was offered £25,000 (NZD $51,000) by a member of Fury's entourage, telling the Mail on Sunday: "I have never kept wild boar. I have never killed a wild boar."
Asked if he had been willing to commit perjury for the Furys, Carefoot said: "I suppose if I'd had to. I was in too deep. They were dangling this carrot. I thought, you're going to get 25 grand for this, it's not a hanging matter. So I went along with it."
Carefoot says he was never paid the money he was promised. "I feel sick of the lies and deceit and the public need to know the truth."
In a statement, UKAD said: "We will always review any potential evidence in relation to any anti-doping offence, and take investigatory action where necessary. If anyone has information that could be of interest to UKAD and its investigations on any matter, we urge them to contact us."
Tyson Fury is yet to respond to the claims but his co-promoter, Frank Warren, hit back at Carefoot, saying in a statement: "The farmer making these outrageous allegations sent me a letter last October, full of errors and basically telling me he had committed perjury by signing statements under oath and lying. When I called him, he asked for money. I told him to clear off and get in contact with UKAD. He chose not to speak to UKAD but instead speak to a newspaper.
"How anybody can take this man seriously is beyond belief. Tyson has never met this man in his life. What a load of rubbish. We'll leave this with UKAD to look into and don't expect it to go any further.
"It looks like while the football season has been paused, there's nothing to write about and silly season has instead commenced."
The timing of the allegations could not be worse for Fury, who remains unbeaten in 31 pro fights.
Having risen from the depths of alcohol, drug and severe mental health challenges after dethroning Wladimir Klitschko in 2015, Fury is widely considered the world's premier heavyweight.
Last month he finished American Deontay Wilder with a stunning seventh-round victory to claim the WBC crown.
Fury and Wilder are scheduled for their third clash in Las Vegas in July. Beyond that, Fury could face a unification bout against Anthony Joshua in what would be one of boxing's richest fights.
WBC president Mauricio Sulaiman gave Fury his backing but UKAD may have the ultimate say.
"Personally, I prefer to believe Tyson Fury ahead of someone who has already admitted to lying in legal documents for financial gain," Sulaiman said. "The person who has claimed he accepted money to lie should be the one on trial, in my personal opinion, especially when he has waited five years to tell his story.
"Secondly, around this time Tyson was not involved with the WBC, he did not fight Klitschko for the WBC belt, it was for other titles, so this issue does not impact on him being our heavyweight world champion."