The former heavyweight world champion has decided against taking an immediate rematch against Daniel Dubois following his defeat in September and the Matchroom chief thinks that a defeat to Fury next year could be a swansong for Joshua.
Asked about the possibility of a 'farewell' bout for Joshua against Fury, Hearn told Sky Sports: "If he got beat, without a doubt.
"What I don't know the answer to is [what happens] if he beats Tyson Fury."
Hearn - whose son Eddie has promoted Joshua throughout his professional career - believes that the British rivals should clash at both Wembley Stadium and in Saudi Arabia before making a decision on their futures in the ring.
He said: "If it came about, because it is so humongous and we do have a responsibility to British fans as well, my own personal feeling and it is not going to make the decision for Joshua, is that should be two fights.
"It should be one in Riyadh, one in Wembley and then both can sit down and say, 'Do you fancy any more or have we made enough?'.
"I don't know what will happen because these are warriors, they are not normal people.
"Their burning desire is to be champion, both of them, but our burning desire is to supply fights that the British public want to see and there is no fight bigger.
"Irrespective of belts, there is no fight bigger than Tyson Fury and Anthony Joshua."
Hearn believes that Joshua is at a "pivotal" career juncture as he approaches his final fights without holding a world title belt.
The promoter said: "It is a pivotal point in his life. He has made a huge amount of money but he is coming up for 36.
"It is a tough loss to take on. As the warrior that he is, he will want to avenge that loss but he also doesn't want to finish his career until he has shared a ring with Tyson Fury because we have been talking about it for 10 years."