Filip Hrgovic, the new IBF world heavyweight champion, has offered a candid insight into the ordeal he endured before beating Moses Itauma in a shock stoppage victory last month, revealing he absorbed so many heavy punches in the first eight rounds that he felt headaches for a number of days afterwards.

“I felt fucked up,” said the 34-year-old Croat. “I received a lot of shots and I was bruised. I had a bit of a headache for a few days. On the Wednesday after the fight I was back in the gym, working out already, but for a few days I felt really tired and bruised, with some headaches.”

Hrgovic, who aims to unify the heavyweight division, also said there is a chance he might face Rico Verhoeven, the Dutch fighter who used to be the world kickboxing champion, on the undercard to the much-delayed bout between Anthony Joshua and Tyson Fury that is expected to finally take place in Cardiff on 11 December.

But revisiting the aftermath of the brutal Itauma bout which changed his life, Hrgovic said: “I didn’t celebrate. I just went home to rest. It was such a hard fight I didn’t even do my tradition after I win, when I go to McDonald’s. I didn’t have the strength.”

Hrgovic believes Itauma is so skilful that, if he learns from his painful defeat, the 21-year-old British prodigy can become unbeatable: “He’s really good. He’s special. Very fast, very talented and he countered whatever I tried with his speed and timing. I never was in the ring before with such a talented kid, with such a fast guy. You have some fast guys but they’re small heavyweights. You can handle them with your power but this kid is fast and big. He’s got great IQ and great talent. If he recovers from this loss, mentally, it will be hard for anyone to ever beat him again.”

Itauma is a complex character and Hrgovic suggested that doubts remain about his mentality. “We’ll see. It was a big shock for him, a big humiliation so maybe it’s the end of his career if he’s not mentally tough. A lot of people, after that kind of loss, never come back. It will be a hard journey for him to come back but if he recovers and he does not lose his confidence then, with this experience, I think no one will ever beat him again.”

Since his shattering defeat, attention has focused on a comment Itauma made before the fight which implied that he has never sparred for 12 successive rounds. Hrgovic said: “It’s not about physical preparation. It’s about experience and mentality. If we go for a run now, or we’re in the gym together, he’s in tremendous shape. He will beat me in every exercise, running, hitting the heavy bag. I think he was physically ready but it’s the mental part. It’s experience.”

Hrgovic, however, compared his own preparation with the less hard-edged approach of Itauma. “You have to go through a ruthless, hard training camp. You need to go through hell to be mentally ready for this shit. Old school is the best school. I told Itauma this before the fight. He’s drinking water, hugging trees in the morning, saying hello to the sun. He does a lot of this bullshit. He’s surrounded by 10,000 yes-men, nutritionists and a coach for sleeping. You can’t get ready for a war this way.”

An exhausted Itauma ran out of energy, after setting a blistering pace, and he was overwhelmed in the ninth round. But the new champion said “I’m still kind of angry because he outboxed me. In my whole career, in 20 years of boxing, I was never outboxed in any sparring or any fight. I was always competitive. But this kid outboxed me. On that night, I think he will beat anyone apart from myself. But that night I refused to lose.”

But, right now, Hrgovic is relishing his rise to world champion: “If I knew it would be so good I would have won the championship before. It’s amazing to be world champion. I want to unify the division and stay here as long as possible. I feel great.”