“If this drags on to September, October, November, December, we’ll have fighters that have not boxed this year,” said Hearn.
“The fighters at the top end are going to be fine but the fighters coming through, small hall fighters, ones starting their careers or those who do not have a sponsorship deal face big concerns.
“They will have to give up the sport of boxing and get a job and that’s heartbreaking for someone trying to live their dreams.”
The British Boxing Board of Control (BBBofC) said on Monday it had extended a ban on all events under its jurisdiction until the end of April.
The Tokyo Summer Olympics, which many amateurs use as a platform before turning professional, look likely to be postponed a year to 2021.
“Look at the Olympics — these people have grafted for four years to achieve their dream and fight in Tokyo,” commented Hearn.
“There’s no chance of these Olympics taking place so what are they going to do? Everything is going to be a complete reshuffle of every sport.”
Joshua, the WBA, WBO and IBF champion, is due to fight Bulgaria’s IBF mandatory challenger Kubrat Pulev in June but that fight could slip to July or later but everything is still up in the air.
Hearn, who has canceled or rescheduled a number of other fights with no certainty of those happening, said boxing would survive but the same could not be said for all the promoters and businesses.
“If you don’t run a sustainable business, very quickly this is going to unfold on you like a ton of bricks,” he said.
Reporting by Alan Baldwin, editing by Ian Chadband