Tyson Fury's first defeat would be inflicted by Frank Sanchez, who has made an 'extraordinary rise' towards a world title shot, says the Cuban's manager Mike Borao.
Sanchez is within striking distance of WBC champion Fury, having propelled himself up to No 6 in the WBC rankings with 19 victories, including 14 wins in the first two years of his pro career.
The 29-year-old trains alongside Saul 'Canelo' Alvarez in Eddy Reynoso's gym and can take another step towards a world title fight when he returns against Carlos Negron in Florida on New Year's Day.
"Frank Sanchez is one of the most active high-profile fighters today," Borao told Sky Sports.
"Frank was the co-main event for Fury vs Wilder III, he has featured on Canelo's pay-per-view fights, and he is now co-main event for the Charles Martin vs Luis Ortiz pay-per-view fight.
"His rise has been extraordinary, as well as his undeniable talent."
Asked whether Sanchez could threaten Fury, Borao told Sky Sports: "I think Frank Sanchez beats Tyson Fury today."
Fury wants his next fight to be scheduled in early 2022, but the WBC has still not announced Dillian Whyte as his mandatory challenger, leaving him without a confirmed opponent for a swift return.
He told Sky Sports at the weekend: "I'm not really interested, because to be honest it doesn't really make much sense who I want to fight at this moment.
"It's who's available and what makes sense later on."
Sanchez staked his claim as a serious challenger by flooring Efe Ajagba, a fellow unbeaten rival, in a dominant points victory on the undercard of Fury's recent knockout win over Deontay Wilder.
Borao, who also manages the career of Charles Martin and advises Robert Helenius, believes that Sanchez will be impossible to avoid if he maintains his relentless progress.
"Tyson is no fool, so I doubt you see a voluntary defence against Frank anytime soon - he will have to force the issue by beating guys like Efe Ajagba and work towards the mandatory," said Borao.
"At Frank's current pace, I have no doubt he will become No 1 contender in short order.
"The day Frank Sanchez gets the opportunity and fights for a world title is the day he becomes heavyweight champion.
"In my perfect world, Charles Martin wins IBF, Robert Helenius wins WBA, and Frank Sanchez wins WBC or WBO world titles in 2022.
"One thing is for sure, I am going to put every ounce of energy I have to deliver for them."