The Sydney Olympic gold medallist said that he will bow out of the sport if the Liverpool fighter successfully defends his British and Commonwealth heavyweight titles.
"I'm now the best I can be and the first guy who beats me at 100%, I will know then that it's over," The Mirror quotes Harrison as saying. "This is that moment.
"If I lose to David Price, I've got no future. It's over. It's over for me as a professional fighter if I lose to David Price.
"This is my door. This is the door I have to walk through. This is the last-chance saloon for me and I would not want it any other way."
Harrison will take on Price in front of a sell-out 8,000 crowd at the Liverpool Echo Arena on Saturday.