"It's a great fight ... Parker is a real threat," Hearn told a British Sky Sports interviewer of Parker's fight in South Auckland in seven days.
"Takam is a dangerous fighter as well. We're going to see what Parker is made of in that fight, and if he wins then on November 19, I believe, the IBF will send a letter out saying Joshua must fight him.
"So we haven't got one eye on that fight, we've got all eyes on it.
"Joshua v Parker in time could be a big fight, but don't rule out Carlos Takam in that fight."
With Joshua, Tyson Fury and David Haye in England, plus lesser heavyweights such as David Price, Dillian Whyte and Dereck Chisora, it is clear where the money is now. Joshua, 26, unbeaten in 16 pro fights, sells out the 20,000-seat London O2 Arena in minutes and will likely fight at Wembley should his star continue to shine.
It has Parker's promoter Dean Lonergan thinking his man is likely to fight out of the English capital should he follow a similar trajectory.
"If Joe did beat Joshua then I can see him fighting in London for two years because that is where the market is," Lonergan said. "You have David Haye and Tyson Fury there, plus Joshua, all big and popular fighters, and I believe the British public and media will take to Joseph too."
Lonergan experienced the Joshua effect in person when he was at last month's fight between the Olympic gold medallist and Martin, who entered the ring in a crown and left thoroughly chastened after being flattened twice in the second round.
But while he was one of the poorest-quality champions in recent times, there is no doubting the power Joshua has in both hands.
"That was invaluable for us to get to see what the Joshua mania is like in London," Lonergan said. "We were four or five rows back from the ring and the atmosphere, the fervour, in the arena was unreal."
While Lonergan is paid to consider all opportunities for Parker, there is no doubt Takam is a far more challenging opponent than Breazeale, hand-picked by Joshua's promoters as close to a sure thing.
"Joseph has to get past Carlos Takam first, of course, and this fight next week I believe is the most important fight to be held in New Zealand. It will unlock doors to the big time and it has been done by mainly fighting in New Zealand. Many people said it couldn't be done - it has never been done before - and certainly David Tua couldn't do it."