The case centres on the fallout from 31-year-old Opetaia’s decision to sign with Zuffa Boxing, the new promotion launched by UFC president Dana White and Saudi Arabian-owned Sela and American company TKO.

Opetaia’s first fight under the promotion came against Brandon Glanton in Las Vegas in March. His IBF world title was due to be defended on the same night that Zuffa Boxing introduced its inaugural cruiserweight championship belt.

According to the complaint, the IBF initially approved those arrangements, accepted a $73,000 (£54,000) sanctioning fee and appointed an official to oversee the contest, before withdrawing its sanctioning less than 48 hours before fight night.

The lawsuit argues the IBF later treated the contest as a title unification because a Zuffa Boxing belt was also being contested.

Opetaia disputes that interpretation, arguing the organisation had already accepted the Zuffa belt was merely a “trophy or token of recognition”, rather than the championship of another sanctioning body. He says there was no legitimate basis for the IBF to reverse its position.

The filing says Opetaia was “placed in an impossible position” by the late decision, forcing him to choose between withdrawing from a contest he had spent months preparing for and losing “his seven-figure compensation”, or proceeding with the fight and “risk being stripped of his championship”.

Opetaia chose to box, defeating Glanton by unanimous decision, before the IBF subsequently vacated his title.

The lawsuit further alleges the IBF’s actions were “the product of coordinated, industry-wide collusion designed to penalise Jai for signing with Zuffa Boxing and to deter other athletes from doing the same”.

There is precedent of a fighter being reinstated as a world champion following legal action.

In 2004, the WBC was forced into liquidation after losing a £17m legal battle against former champion Graciano Rocchigiani.

Rocchigiani won the WBC’s vacant light-heavyweight title in March 1998 after it had been relinquished by Roy Jones Jr.

But Jones decided he wanted to keep the belt and the WBC reinstated him as champion in June 1998.

In addition to the compensation, the WBC was ordered to recognise Rocchigiani as champion from 1998-2000.