Romero was set to fight against David Branch at UFC Orlando on February 24, he will now fight two weeks earlier than expected, this time for the interim-title.
Whittaker suffered an undisclosed injury while training for his first ever title defense against Luke Rockhold at UFC 221 and will be unable to compete, UFC confirmed on Saturday morning.
Whittaker's injury was first reported by ESPN's Brett Okamoto on Friday with additional news that Yoel Romero will be stepping up to face Rockhold instead.
Rockhold (16-3) will now face Yoel Romero (12-2) for an interim 185-pound championship.
UFC 221 takes place on February 11 at the Perth Arena. "I hope the fans enjoy what should be a great night of fights at UFC 221, and I look forward to a recovery as soon as possible that will have me back in the Octagon to face the victor of the main event".
The top-ranked middleweight issued a statement on social media saying that he had been ruled "medically unable" to fight at next month's event.
"I would like to apologise to all my supporters and fans of MMA for not being able to put on the show you deserve", Whittaker wrote on his Instagram account.
Whittaker first won the interim title in July of previous year, elevated to the undisputed champion after newly crowned king Georges St-Pierre - who defeated then-champ Michael Bisping at UFC 217 in November - elected to vacate the throne after being diagnosed with ulcerative colitis. Rockhold and Romero competing for an interim strap further signals to said return, but Whittaker suffering an injury is unfortunate nonetheless. It was the former champ's first fight since losing his middleweight belt to Bisping at UFC 199 in June of 2016.