Wladimir Klitschko has described Anthony Joshua as a fighter who gets confidence from his “big muscles” and suggested that will ultimately not be enough for the 27-year-old to hold on to his IBF title when the heavyweights meet at Wembley this month.

A crowd of 90,000 people are expected to fill the national stadium on 29 April for one of the most anticipated bouts of the year and for Klitschko it represents a chance for redemption following his defeat to Tyson Fury in November 2015. The 41-year-old former WBA, IBF and WBO champion has not fought since while Joshua has gone on to stretch his record to 18 wins from 18, all via knockout, and in the process become a world champion himself.

Klitschko is full of admiration for the 2012 Olympic gold medallist, particularly so having sparred with him three years ago, but speaking at his training camp at the Stanglwirt hotel in the Austrian Alps on Wednesday, the Ukrainian outlined his belief that his opponent, while intimidating and impressive, is ultimately limited and “raw”.

“AJ has a lot of energy, he’s young, he wants to show it. He has these big muscles that give him confidence,” said Klitschko. “He wants to demolish people, but did you hear about boxing? It’s the sweet science. The ice is thin and the most vicious boxers get conquered. I have a lot respect for Anthony – his commitment and physical ability. He can lift weights, he’s strong. He can be a cross-fit world champion actually. But cross-fit is not boxing.”

Klitschko was in relaxed mood as he spoke at a venue he has used as a preparation base since 2003, but the veteran, who will be contesting his 68th fight – and 29th world title contest – became noticeably agitated when it was put to him that Joshua may be making a mistake facing him given their respective levels of experience.

“A mistake? No. I’m sorry, should I wait another five years? I can’t,” he said. “The opportunity is now, I don’t want to hear, ‘Oh, it was too early for him’ or ‘Klitschko is over the hill’. Everything has its time.

“I think it’s going to be a great event. I hope both fighters get through it injury free, so there are no other issues.”

•Sky Sports Box Office will show Joshua v Klitschko exclusively live on 29 April. To book go to www.skysports.com/joshua