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Oleksandr Usyk, the former cruiserweight king who is scheduled to make his debut at heavyweight this Saturday in Chicago, will face Chazz Witherspoon in a late-replacement fight. This comes after Usyk's originally scheduled opponent, former kickboxing star Tyrone Spong, tested positive for a banned substance. DAZN announced the new fight on Twitter on Tuesday.

Matchroom's Eddie Hearn announced on Monday that VADA had returned an adverse finding for Spong (14-0, 13 KOs) in their drug testing, temporarily leaving Usyk (16-0, 12 KOs) without a dance partner. Hearn did say they had options for replacement opponents lined up, and it Witherspoon eventually stepped up to fill the role.

Witherspoon (38-3, 29 KOs), the man tapped for the job, brings a lengthy resume -- though against lower-tier opposition -- to the bout. He is currently riding an eight-fight winning streak since losing a shot at the NABO title against Seth Mitchell in 2012. Witherspoon has only fought twice since 2018.

Usyk's move to heavyweight is highly anticipated after he became the first man in history to hold all four major championships at cruiserweight. He ran through the deep field of the World Boxing Super Series, knocking off Marco Huck, Mairis Briedis and Murat Gassiev, all in their home countries, to win the tournament. He wrapped up his cruiserweight career by traveling to England to knock out Tony Bellew last November.

As Usyk was the WBO's "super champion," he was immediately made the mandatory opponent for the winner of the Dec. 7 rematch between Anthony Joshua and champ Andy Ruiz Jr. in Saudi Arabia.

Usyk was originally scheduled to face Carlos Takam in his heavyweight debut in May, but was forced to withdraw from that bout with a biceps injury. The two teams hoped to reschedule the bout for September, but Takam signed on to fight Craig Lewis instead.