Oleksandr Usyk has been released after being detained in Poland on Tuesday night.
A video emerged on social media of the unified world heavyweight champion in handcuffs at Krakow airport before the Ukrainian's expected arrival in London for the Anthony Joshua vs Daniel Dubois fight at Wembley on Saturday.
ESPN have reported that Usyk was deemed not 'fit to travel' but he was attempting to explain that he was 'exhausted' after 14 hours of travelling from Kyiv in Ukraine. Usyk later took to Instagram to say it was "a misunderstanding" with local police.
He wrote: "Dear friends, a misunderstanding took place.
"It was quickly resolved. Thanks to all who got concerned.
"Thanks to Ukrainian diplomats for the efficient support.
"And respect to Polish Police for conducting their obligations with no regards to height, weight, reach and regalia.
"Thanks God to everything."
Sky Sports News has reached out to Usyk's management for further clarification on the circumstances.
Ukraine president Volodymyr Zelenskyy said on Telegram: "I spoke to Oleksandr Usyk on the phone when he was detained.
"I was outraged by this attitude towards our citizen and champion.
"I instructed the Minister of Foreign Affairs of Ukraine Andriy Sybizi and the Minister of Internal Affairs of Ukraine Ihor Klymenko to immediately investigate all the details of the incident at the Krakow airport.
"As soon as I was informed that everything was fine, our champion was released and no one else detained him."
Usyk targeting Joshua vs Dubois winner?
Usyk's presence at ringside will ramp up speculation that the WBC, WBO and WBA champion could face the Joshua vs Dubois winner in a future undisputed world title fight.
The 37-year-old is preparing for a rematch against Tyson Fury in Riyadh, Saudi Arabia on December 21, having defeated the British star in May to unify all four major titles.
He relinquished the IBF belt in June, which meant that Dubois was elevated from 'interim' to full IBF champion.
Joshua suffered back-to-back points defeats to Usyk, while Dubois was stopped by the supremely skilled southpaw, but both Brits will harbour hopes of gaining revenge and every world title in another fight.
Fury is also set to attend Joshua vs Dubois this weekend.
Anthony Joshua's heavyweight showdown with Daniel Dubois takes place on Saturday September 21 live on Sky Sports Box Office. Book Joshua v Dubois now!
