Oleksandr Usyk's reign as undisputed world heavyweight champion is already over but could he lose more belts?

Oleksandr Usyk's reign as the undisputed world heavyweight champion was brief after he handed back the IBF belt, but will more belts be ripped away?

The Ukrainian star produced a spectacular victory over Tyson Fury in May to unify the WBC, WBA, IBF and WBO titles, but just a month later, his reign as the undisputed king was over.

Contracted to rematch Fury in December, Usyk was unable to make a mandatory defence of the IBF belt, that meant Daniel Dubois, the organisation's Interim belt-holder, was upgraded to full champion in June.

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Usyk confirmed he was relinquishing his IBF title with a video on social media and Anthony Joshua will challenge Dubois for the IBF belt at Wembley on September 21, live on Sky Sports Box Office.

Could Usyk's other titles be under threat?

Former champion Joseph Parker earned a WBO Interim heavyweight strap in March when he beat Zhilei Zhang and the New Zealander can push for a mandatory shot at the full world championship.

Parker is "next in line" for a crack at the WBO belt, according to his promoter David Higgins.

He told Sky Sports in April: "Every boxer should want the world title shot.

"Joseph would love to fight the [Fury vs Usyk] winner of course but that's not necessarily to say it would happen yet."

The WBA has a 'regular' heavyweight belt-holder, Mahmoud Charr, who harbours his own ambitions of fighting for a major title.

Michael Hunter also earned the WBA 'Gold' title after a points win over Cassius Chaney.

Sky Sports has contacted the WBO and the WBA to comment on whether Usyk is in danger of being stripped of their belts too.

The WBC has not named a mandatory challenger for its heavyweight championship.

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Agit Kabayel won an elimination bout on the Fury-Usyk undercard, but it was not a final eliminator and the WBC confirmed to Sky Sports that its world championship will remain in Usyk's possession and be on the line in his December rematch with Fury.

"The WBC granted the sanctioning of Usyk vs Fury 1 with a rematch. The rematch is supposed to take place in December and after that the WBC has absolutely no mandatory contender at this time in any formal manner," WBC president Mauricio Sulaiman told Sky Sports.

"The WBC sanctioned an [Kabayel vs Sanchez] elimination bout as requested by the promoters. He defeated Frank Sanchez, who had been in the top positions for many years and looked great.

"So he has won already two times in Saudi both by knockout, both have been against top-five contenders. He deserves absolutely to be in a very privileged position and as I mentioned right now the WBC only has the rematch between Fury and Usyk as a sanctioned event, anything further will have to be dealt with by the board of governors."

Will we see another undisputed fight?

Sulaiman certainly does not rule out the WBC sanctioning a future fight between the Usyk-Fury rematch winner and Joshua if he overcomes Dubois to claim the IBF belt.

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"Joshua has been in the limelight for a decade, especially outside the ring he is a very special person and he represents the best of boxing inside and outside the ring," Sulaiman said.

"Anthony Joshua is a very special unique fighter that has been closely associated with the WBC for many, many years. He was the WBC International champion, he defended it several times.

"The WBC was the first organisation to rank him, to rank him in the top 10, the top five. In fact when he fought [Charles] Martin for the IBF title he was the No 2 contender of the WBC. Destiny brought him to another organisation and a different route.

"But we have always had great esteem, respect and admiration for Joshua.

"Joshua is there and Kabayel is there. We're not promoters so we cannot stage fights. We are being very lenient, very flexible to not interfere.

"We want the best fights made, that's it."