Joshua secured his 20th win on Saturday night, earning a 10th-round stoppage against France’s Carlos Takam, himself a late replacement for the injured Kubrat Pulev.
But the Brit’s win was not the comprehensive knockout fans have become used to and Warren was quick to criticise the performance.
In fact, the promoter believes he has already identified the man to end Joshua’s run – Daniel Dubois, a 20-year-old whose first five fights have all ended in knockouts and in total just seven rounds.
“Dubois is the best heavyweight prospect I have ever seen at this stage," Warren told the Telegraph.
Joshua vs Takam: The moment the ref STOPS the fight
Sat, October 28, 2017
This is the moment the referee stopped Anthony Joshua’s stunning heavyweight fight with Carlos Takam
Action Images via Reuters
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Anthony Joshua's heavyweight title fight with Carlos Takam is stopped by the ref
“There are obvious fights out there with Deontay Wilder and Joseph Parker, the two other champions, but my man Daniel Dubois is very talented.
“Look, I don’t go crazy about young fighters because there is always a long way to go – but he is by far the best heavyweight at this stage of his career that I have seen in my time in boxing.
“He has a fantastic jab, real power, he's relaxed, a natural boxer and puncher.
“Not only did he knock Joshua down [in sparring], he absolutely did for Joshua in the gym, as he has done with all the names he has sparred with."
Anthony Joshua was apparently completely out-boxed in sparring by Daniel Dubois
Anthony Joshua beat Carlos Takam but some were not impressed with his performance
Joshua's promoter Eddie Hearn has already outlined their plans to fight three times in 2018.
The Brit wants to take on Deontay Wilder and Joseph Parker as well as returning former champion Tyson Fury with the goal of unifying the heavyweight division and installing himself as the undisputed champion of the world.
However, Warren reckons Dubois is just one year away from toppling AJ.
“Do not worry about Joshua running out of opponents," Warren added.
“I think Dubois could be ready in 12 months' time.
“I’d put him in with Parker after five more fights.
“There are always question marks and things to answer but I have a talent here, mark my words.”
Dubois’ next outing will come against Dorian Darch, a Welshman who also faced Joshua in the Brit’s early days, on the undercard of James DeGale’s UK return on December 9.