WBC heavyweight champion Deontay Wilder (38-0, 37 KOs) has fired back at former cruiserweight beltholder and Sky Sports analyst Johnny Nelson.

Wilder was angered after being advised that Nelson conducted an interview with reporters in the UK and claimed that the undefeated puncher was knocked out, twice, during past sparring sessions with Wladimir Klitschko.

Wilder was ringside in late April, when Anthony Joshua stopped Klitschko in eleven rounds to unify the IBF, IBO, WBA heavyweight titles before a record crowd of 90,000 fans in Wembley in London.

According to Nelson, who ringside as part of the Sky Sports broadcast team for Joshua-Klitschko, the attitude of Wilder - when it came to his willingness to face Joshua - completely changed after watching Klitschko lose.

“His attitude changed,” Nelson said. “Let me tell you this. Wilder had sparred with Wladimir Klitschko on various occasions.

“Wladimir Klitschko knocked him out cold twice and put him down a third time with a body shot. This is the worst kept secret going. Wilder sees what Anthony Joshua did to Klitschko and he thinks, ‘Wow’."

Wilder has responded and took aim directly at Nelson. Wilder, who sparred for 50 rounds with Klitschko, denies that he was ever knocked out or dropped by a body shot. And he also denies the claim that his attitude changed when it came to have a unification with Joshua.

"He said that me and Klitschko sparred on various occasions, and in fact that Klitschko knocked me out cold and dropped me with a body shot. Keep in mind that Klitschko hasn't thrown a body shot in eleven damn years. All of a sudden it had to be me. Why me? I had to be dropped in sparring. I was only in the Klitschko camp one time and I held my own very well with everybody," Wilder said.

"All of a sudden this mysterious untold story of me and Klitschko [comes out] and he knocked me out, c'mon man. Please, people with bitch tendencies. I'm the wrong man to spread rumors about and lies. Then you go on to say that I went to the AJ-Klitschko fight with 90,000 people and all of a sudden my attitude changed, that I had a willing heart to fight AJ. What are you talking about? I had that same willing heart since I touched my feet on your soil.

"Then you said that after Joshua beat Klitschko, that my attitude changed that I knew that it wasn't going to be a soft touch fight anymore. My dude, what's the difference between Tyson Fury beating Klitschko and AJ [beating him]. Fury had an easier time with Klitschko. If anything I think that I'm going to whoop that ass. Don't hype these people up Johnny. If you're going to do it, at least the say truth about it.

"The only thing that I thought about when I saw that fight, is how I'm going to whoop his ass like Norbert Ekassi KO'd your ass in 1992 my dude. Boxing may have originated in the UK, but those belts are going back to the USA, trust me."