Volkanovski's featherweight bout with Californian Brian Ortega was set to co-headline to the March 28 event alongside a heavyweight showdown between Stipe Miocic and Francis Ngannou.

It's no longer on the card, with ESPN UFC announcer Brendan Fitzgerald confirming live on UFC Fight Night on Sunday that the fight has been postponed.

Volkanovski's management subsequently confirmed the positive test result, a devastating blow for Volkanovski whose long-awaited title reign has been beset with disruptions due to the pandemic.

In a statement, Volkanovski's team reported he left Australia on 14 March 14 having tested negative and tested negative on arrival in the US before entering the UFC bubble.

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However, his most recent test has produced a positive result, resulting in the postponement of the bout.

"We have worked so hard to be ready for this fight and I am absolutely devastated this has occurred," Volkanovski said.

"We followed every policy and process to remain COVID free but it wasn't meant to be at this time. The support we have had since arriving has been amazing and we can't thank everyone enough who have helped us in preparing for the fight.

Thanks to everyone back home and around the world for your positive messages. Sadly, it isn't to be this time. To my fans, I'm certain I'll be bouncing back stronger than ever before."

The pandemic had kept Volkanovski to just one title defence, a razor-thin split decision win over the man he convincingly dethroned, Max Holloway, in Abu Dhabi in July last year.

It's his only bout since taking the title from Holloway by unanimous decision in December 2019. The second bout came on 'Fight Island' in front of no fans amid the strictest of protocols.

Strict protocols remained in place ahead of UFC 260, but it's now a futile trip, with the champ to head home to Wollongong without defending his belt.

It's also a frustrating development for Ortega, who was out of action for two years before returning with a convincing points decision win over Chan Sung Jung in October that earned him second shot at UFC gold.

The pair have showed each other plenty of respect in the build-up and that continued following the news, with Ortega taking to Instagram to wish his rival the best.

"He's done everything right, we're done everything right," Ortega said.

"[To Volkanovski] I know you would've taken the fight no matter what, even with COVID. That's the type of human you are and I respect that.

"I hope you get better, I hope you heal up fast, we'll postpone and reschedule it to when we have to. Stay sharp, we're staying sharp and whenever this shit's meant to happen, it'll happen."

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