This comes one year after Whittaker, in February 2018, was unable to defend his middleweight title against ex-champ Luke Rockhold in Australia due to injury.
In a later statement, UFC said Whittaker had undergone emergency surgery due to a "severe abdominal injury".
Per Okamoto, the hernia was not related to Whittaker's weight cut.More news: Elizabeth Warren officially kicks off 2020 White House bid
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Other fights on the UFC 234 main card include Rani Yahya vs. Ricky Simon (Bantamweight), Montana De La Rosa vs. Nadia Kassem (Women Flyweight) and Jim Crute vs. Sam Alvey (Light Heavyweight).
Silva was guaranteed a title shot by White if he defeats Adesanya at UFC 234 at Rod Laver Arena in Melbourne this weekend.
Elevated to the co-main is the lightweight matchup between Albuquerque action hero Lando Vannata and surging Brazilian Marcos Mariano.
Gastelum's manager has stated that he hopes Kelvin will fight the victor of Silva vs. Adesanya for the title in his next octagon appearance. We still will be getting what should be a stellar middleweight showcase in the main event with a prominent name attached - it just won't be contested for the 185-pound title.