Heavyweight contender Chazz Witherspoon is promising a big shocker this Saturday.

Earlier this week, Witherspoon replaced Tyrone Spong as Oleksandr Usyk's opponent for his heavyweight debut in Chicago.

Spong was denied a boxing licence by the Illinois State Athletic Commission after there were adverse findings in two of his urine tests. The unbeaten puncher has denied taking any performance enhancing drugs.

Usyk's heavyweight debut has been postponed from May, when he withdrew with injury from a planned bout with Carlos Takam. 

Witherspoon, who has a 38-3 record with 29 knockouts, tasted his last defeat in 2012 when he was stopped by Seth Mitchell.

Most observers expect Witherspoon to get blown out by Usyk, who won Olympic gold in 2012 and unified the entire cruiserweight division in 2018.

Witherspoon has promised to prove everyone wrong - including Usyk and his handlers.

“So many people on the internet are talking badly about me, asking me why I got this shot. But it’s all about my team. I am not with a big time promoter and there’s no red tape in my career. I trust everyone around me. I am now at a point where I need to take this shot. There’s a huge opportunity for me here. It came knocking and I opened the door to see who it was, and here I am. Usyk is a great guy, I have the utmost respect for him," Witherspoon said. 

"I am not one to get up here and talk crazy. That’s not me. I am a guy that is going to show up and rumble. I’m never scared, my heart don’t pump Kool Aid. I am the bigger guy and I am going to come in there and mix it up. I am looking for lightning to strike here, but I am coming to rumble.”