Tyson Fury has claimed he does not need to get fit to beat Anthony Joshua, labelling him "useless" and a "bum" in response to the heavyweight champion's Twitter insult.
Fury has been goading potential opponents Deontay Wilder and Joshua in recent weeks as he claims to be embarking on the long road to a competitive comeback.
The 29-year-old, who stunned Wladimir Klitschko in November 2015, has gained a significant amount of weight since vacating his belts and having his boxing licence revoked last year amid a failed drugs test and mental health issues.
Joshua posted a tweet on Thursday telling Fury to "get fit you fat f***."
And his outspoken fellow Briton could not resist returning fire via an Instagram video.
"This is a message to… the weightlifter," he said.
"Big Anthony Joshua. The big tough man. That told me to 'get fit, fat f***'. It's a new one, because he normally doesn't swear. Tries to not be himself. So you've been yourself now, which is good.
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"To be honest with you, me old mate, I don't need to get fit for somebody like you. At all. I could come to you and I'll punch all your face right in to you. Even at 25 stone. So, I really don't need to get fit for you, anyway, put it that away. I've seen what you're about. You fought a midget the other day… the referee had to stop it in case you got caught or beat. Bum city, like I always said.
"Useless, no gas, no stamina, too many weights. You want to practice on a bit more speed and less power. Bum!"
In a caption accompanying the video, Fury told Joshua: "I do not care about you! Like I told you before I'll punch your face in bad boy.
"Fighting to me is easy & slapping punks like you is even easier. Good to see [promoter] Eddie [Hearn] has let you of your leash for the day. But he Better put you back on before u get bitten."