The New Zealander will face Chisora on May 1 and Hearn has suggested that a victory would move him into prime position to contend for the world championship belts next year once Anthony Joshua and Tyson Fury have completed their fights.
He told Sky Sports: "That's just going to go off, from the first bell, that fight.
"Actually, Joseph Parker is right up there, since his win over Junior Fa. He's top five, top six with a couple of governing bodies now.
"If he beats Chisora, when these belts become fragmented in probably 2022, this is a really important fight for him."
Hearn expects entertainment from the fight as he expects it to be Chisora's last chance to show he can compete at the top of the heavyweight division.
He said: "For 'Del Boy', of course it's the last roll of the dice, in a big, big heavyweight fight.
"When has he not given us anything but unbelievable entertainment?
"It doesn't matter whether it's Dillian Whyte 1, Dillian Whyte 2, Szpilka. Takam was one of the most exciting fights I've ever seen. Usyk here and the Parker fight will be no different."
Hearn continued: "Both guys teaming up with a new training team. Great, great men. Andy Lee, of course, in Joe Parker's corner, and Buddy McGirt in Chisora's corner. It's going to be an interesting battle."