#2. Jon Jones, UFC 151
The new generation of MMA fans might not appreciate just how great Dan Henderson once was. The retired MMA legend is one of the best fighters to have never won a UFC title.
However, at UFC 151, he was scheduled to fight Jon Jones in what would have been the penultimate title fight of his career. Unfortunately, a crippling knee injury forced him to withdraw from the bout 8 days before the fight.
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Desperate to find a replacement opponent for Jon Jones, Dana White elected to have the then longtime middleweight contender Chael Sonnen take Henderson's place. In a move that stunned the MMA world, Jones declined to face Sonnen on such short-notice, with former coach Greg Jackson claiming that the bout would have been the biggest mistake of Jones' career.
The fight card was too thin to survive without its headline bout, and the whole event was ultimately canceled, with White blaming 'Bones' for the debacle.
#1. Khamzat Chimaev, UFC 279
Despite the fact that Khamzat Chimaev has defeated higher-ranked opponents compared to the unranked Nate Diaz, his expected win over the Stockton legend at UFC 279 would have been the crowning achievement of his career due to Diaz's starpower.
Unfortunately, the matchup never took place. Even the pre-fight press conference was scrapped, all due to Chimaev's shenanigans.
A brawl between 'Borz' and divisional rival Kevin Holland ensued backstage, which worsened when Nate Diaz and his entourage brawled with Chimaev's posse.
The resulting chaos was enough to convince Dana White to cancel the press conference altogether. Worse still, the Chechen phenom failed to make weight for his welterweight bout with Diaz.
Not only was Chimaev 7.5 lbs over the welterweight limit, but his blunder led to a massive reshuffling of the fight card. Nate Diaz was forced to face Tony Ferguson. Ferguson's previously scheduled opponent Li Jingliang was booked into a matchup with Kevin Holland's foe, Daniel Rodriguez. Meanwhile, Holland faced Chimaev himself, who was demoted to a co-main event spot.