Eddie Hearn admitted that Francis Ngannou made him tremble and that he presents a risky opponent for Anthony Joshua.
Joshua faces Ngannou this Friday, live on DAZN PPV, in Saudi Arabia.
For Joshua it is a chance to win his fourth successive bout as he comes back from twin defeats to Oleksandr Usyk.
And for Ngannou, it is an opportunity for his first win in the boxing ring after a split-decision loss to Tyson Fury in October. Fury and Usyk fight for the undisputed title on May 8, also on DAZN PPV.
Speaking to Sky Sports, Hearn said believes Joshua knows he has a job to do, but admitted Ngannou is a powerful threat.
Hearn said: "The landlord is in town to collect his rent, that's what it is. Come over. Knock Ngannou out. Do a job. Get paid. Go back and smash up the winner of Fury-Usyk.
"Some call us deluded but that is the mindset. Anthony Joshua is going to be undisputed champion but he has this massive hurdle in front of him on Friday night.
"It is a massive risk against little reward because most people are expecting him to beat a UFC fighter.
"[Ngannou] is probably more than a UFC fighter. We saw in the Fury fight someone that was very competent, very confident, someone with huge power who is incredibly strong.
"I'll be honest with you, the knees were trembling a little bit when I saw the size of him at the grand arrivals. He is a man mountain and he is full of heart. You know AJ has to be switched on."
Live on DAZN: Check your region for the Saudi Pro League. Click here for details.