Anthony Joshua believes Deontay Wilder needs to "stop living the fantasy" if the pair are to meet in the ring.
Joshua will put his WBA and IBF world heavyweight belts on the line against WBO champion Joseph Parker in Cardiff on March 31.
WBC strap-holder Wilder has been touted as the next opponent for Joshua if he comes through his bout with Parker.
"Wilder has to be realistic and stop living the fantasy," Joshua told BBC Sport.
"If he was serious about the fight, we'd do serious negotiation. If not, stop hooting and hollering because we'll just freeze him out."
Joshua tipped the scales at a career-high 18st 2lbs in his last bout, a defeat of Carlos Takam in October.
And the 28-year-old expects to be lighter when he takes on Parker at the Principality Stadium next weekend.
"Around this time in my last camp, I was around the same weight I am right now," Joshua said.
"I don't know how I shot up in weight in fight week. Maybe I relaxed, maybe I was so exhausted that I lay on the bed eating.
"It went on so easily. I spent three months training every day and then for a week did little.
"I'm learning. Fight week is as important as camp. I won't be coming in that heavy, I really doubt it."
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