Tony Bellew told Oleksandr Usyk "I was born ready, let's get this done" after the history-making cruiserweight called him out on Saturday.
The Ukrainian defeated Murat Gassiev on points in the World Boxing Super Series final in Moscow to become the first man to hold all four cruiserweight world titles at the same time.
Usyk quickly turned his attention to Bellew after outclassing the previously unbeaten Gassiev to claim the inaugural Muhammad Ali Trophy - even declaring his willingness to "eat more spaghetti" if the fight needs to happen at heavyweight.
"First of all, we need to take a rest after this difficult fight. After that, I will sit with my team and we will make a decision," he said in his post-fight interview.
"At this time, I have heard that Tony Bellew wants to fight the winner of the Muhammad Ali Trophy. I hope he will see me talking.... 'hey Tony Bellew, are you ready?'
"If he doesn't want to go down [to cruiserweight], I will go up for him. I will eat more spaghetti for my dinner!"
Bellew stated it would need to be "something absolutely ridiculous" for him continue his boxing career following back-to-back wins over domestic rival David Haye.
However, the Englishman wasted no time in accepting the challenge, tweeting: "Usyk I was BORN READY!! Let’s get this done!!"
Usyk simply replied: "I'M ALSO READY."