The Briton takes on Andy Ruiz Jr tonight in his American debut, a fight he is heavily expected to win.
Joshua is defending his WBA, WBO, IBF and IBO world heavyweight titles, two of which he won against Klitschko in their thrilling fight at Wembley Stadium.
But ‘AJ’ has told head coach Rob McCracken that he would retire if he ever had to deal with a fight like that again, in a interview to Ireland sports outlet Joe.
Joshua endured his toughest night in the ring against Klitschko, and was knocked to the canvas for the first time in his career.
The Brit was almost stopped at one point in the fight as the Ukranian knocked him back to the ropes before unloading a series of heavy shots.
Joshua survived the round (which round?) before knocking out Klitschko in the 11th round.
However, he explained to former two-weight world champion Carl Frampton that he swore he would never go through a gruelling fight like that again.
“It was a slugfest, it wasn’t even a technical fight where he caught me,” Joshua said. “It was just a slugfest.
“It was one of those where I had to go down to get back up.
“I learned I was too top-heavy as a heavyweight. I was doing my weights and I couldn’t carry my body properly.
”I also learned how to pace myself.
“Most importantly I said to my coach ‘if I have another one of these fights, I’m done with boxing’.
“I said ‘I should be good enough so I don’t have to go through hell and back just to win a fight. It should be good competition but I shouldn’t have to go through all that to win.”
Joshua has his sights set firmly on unifying the heavyweight division, having already dethroned Joseph Parker for the WBO belt.
He told Sky Sports he didn’t want to “rob the fans” of a showdown against WBC champion Deontay Wilder.
“It’s weird, I feel like credibility in the division comes from who is calling who out, rather than who is actually fighting who,” he said.
“So, I don’t need to be negative towards him, good luck to him.
“However, I’m a fan of the sport, I’ve tried to challenge all the best fighters.
“Let’s not rob the fans. I’m a fan of the sport and I feel like I’m robbing myself of a good fight, so good luck to whatever he’s doing, if he still wants to have that conversation he can.”