Hearn says the 26-year-old former WBO boxing champion is a calibre fighter, who can go up against the best in the heavyweight division.
"There is a lot of depth now in the heavyweight division," said Hearn.
"Even the guys that are losing are available for big fights, not with AJ.
"But (Joseph) Parker will come back in a big fight, (Alexander) Povetkin will come back in a big fight."
Joshua defeated Russian boxer Povetkin via a seventh round TKO yesterday at Wembley Stadium, to retain his WBA, IBF and WBO titles.
"The division has never been better and that is down to strength and depth."
Parker lost to Joshua in April via unanimous decision in Cardiff, Wales.
He also lost by unanimous decision to number one ranked WBC fighter Dillian Whyte in July in London.
Parker is expected to return to the boxing ring in December for his final bout in 2018.