The 31-year-old lost his IBF world title to the impressive American, forced to take a knee in the 11th before it was waved off with his left eye almost closed.
Brook suffered a similar injury to his right eye in his previous fight against Gennady Golovkin but Hearn insists Brook he return - although as a super-middleweight (154lbs).
"No excuses in the fight - injuries or weight... he was beaten by the better man," Hearn told sportinglife.com.
"The surgeon was in the ring afterwards and is already very confident about the operation he is going to need. However, it's a big blow to the career of Kell Brook. He went through a lot of pain with the first one and now he's got to go through another one... but that's boxing.
"He's done at welterweight now - he didn't make the weight horrifically for this, he just did it the same way as he's always done in the past. We were quite happy with how he made the weight, but he's 31 now and he deserves a lot of respect.
"I know Errol thinks so because he got to fight the champion in his home town, rather than fighting in Texas against the No 2 or No 3 contender. He showed his grit coming over to the UK and it was all on the line for both of them."
Brook, meanwhile, admits he devastated to have lost in front of his fans at Bramall Lane, but believes he made the right decision in ultimately pulling out.
Speaking to Sky Sports News HQ, Brook said: "They kept me in until about 3am. I had a CT scan on my eye and the eye is broken again, same as the Golovkin one, so, maybe surgery again.
"I'm devastated. I knew from round seven that the eye had gone and progressively as the rounds went on. I tried to get through the fight and it kept going double-vision and then coming back into line.
"In the later rounds 10 and 11, especially 11th round, it stuck there and that's why I went down on one knee and I remember the surgeon saying to me after the Golovkin fight if you would have gone another round or so you could be blind so I've got that going through my mind as well.
"I'm in my own city, I'm in Sheffield. I wear my heart on my sleeve. There were many things going through my mind but I remember thinking I live to fight another day."
