The heavyweight debut of Oleksandr Usyk is running into some turmoil.

Usyk is scheduled to face undefeated heavyweight banger Tyrone Spong, this coming Saturday night in the main event of a DAZN streamed card from the Wintrust Arena in Chicago.

Eddie Hearn, who promotes Usyk, has revealed that Spong tested positive for a banned substance in random drug test administered by VADA [Voluntary Anti-Doping Association].

According to Hearn, there are replacement opponents on standby.

"We have been contacted by VADA to inform us that there has been an adverse finding in Tyrone Spong’s test. It has been sent to the State of Illinois commission and further information will be released in the morning. We have reserve opponents standing by," Hearn stated.

Usyk (16-0, 12 KOs) was scheduled to make his heavyweight debut earlier this year against Carlos Takam, but the Olympic gold medal winner withdrew with injury. Talks to reschedule went nowhere, after Takam signed a promotional deal with Joe DeGuardia of Star Boxing.

In 2018, Usyk unified the entire cruiserweight division when he united the WBC, WBA, IBF, WBO world titles, with a dominating decision over Murat Gassiev in the final bout of the World Boxing Super Series. In his final cruiserweight bout in November of last year, Usyk scored a brutal knockout of Tony Bellew, who retired afterwards.