Anthony Joshua has criticised Tyson Fury for how long it took him to fight for a world title and claimed his rival's career could be approaching its end.
Fury turned pro in December 2008 and won his first world titles against Wladimir Klitschko seven years later in his 25th fight. Joshua needed just three years and 16 fights.
"Fury has been professional much longer than me. He should be looking to retire soon," IBF, WBA and WBO heavyweight champion Joshua told Sky Sports about WBC holder Fury.
"If he wants to cement his legacy, I'm here and ready. I've built myself into this position."
Rival world heavyweight kingpins Joshua and Fury have agreed financial terms to two fights in 2021 that would decide the division's undisputed champion.
First Joshua must defend his belts against mandatory challenger Kubrat Pulev, expected in December, while Fury is contracted to a third meeting with Deontay Wilder.
"I'll challenge Fury, I'll challenge Wilder," said Joshua. "These guys aren't the biggest names that I've fought on my record anyway. They are just another heavyweight.
"Look at my record. They are not the best fighters that I have challenged.
"When they are ready, I'm here to fight."
Joshua ascended from being an Olympic gold medallist at London 2012 to a world champion just four years later but, despite losing his unbeaten record and titles to Andy Ruiz Jr, reclaimed them last December.
"I came up quick. That shows I'm ready. These boys turned professional in 2008 and it took [Fury seven years] to fight for the heavyweight championship of the world," said Joshua.
"He's on a completely different journey. I want to steam through.
"I haven't got fear of Fury - whether he's got a better chin than me, a better jab than me, whether he's all of this stuff that people say. So be it. Let me go in there and prove myself. Show you who I am and what I can do.
"I've fought five champions and been in two unification fights. I'm a two-time heavyweight champion in the space of 24 fights and a [seven-year] career. It shows you I am serious.
"If Fury is serious, I'll take that fight seriously too."
Are there obstacles to Joshua vs Fury?
The most obvious hurdles are their next opponents - Joshua's IBF mandatory challenger Pulev, who has beaten Derek Chisora and Hughie Fury and whose only loss in 29 fights came against Wladimir Klitschko, and Fury's old rival Wilder who comprehensively lost his WBC and undefeated record when they last met.
Dillian Whyte lost his status as the WBC mandatory challenger when he was knocked out by Alexander Povetkin. The WBC have since told Sky Sports that they back an undisputed title fight in 2021: "An ultimate unification would be something that everyone would like to see."
But Oleksandr Usyk still lurks as the WBO mandatory challenger, a status he will risk in his next fight with Chisora.
"He has agreed to let AJ versus Pulev happen, with regards that the winner fights him next," Usyk's co-promoter Alexander Krassyuk, who works alongside Eddie Hearn, told Sky Sports. "This statement is still solid."