Anthony Joshua will hold his world heavyweight titles “for a very long time”, says former champion Wladimir Klitschko.
Briton Joshua, 28, is the IBF, WBO and WBA champion and beat Klitschko by knockout in April 2017.
“We will see how much and how big his desire is to stay successful,” said Klitschko.
“It’s easy to have success for a short period of time but to maintain it for a long time is really challenging.”
He added: “I’m a fan of Joshua so, due to his athletic qualities and age, I think he is going to hold the belts for a very long time.”
Klitschko’s nine-year reign as lineal world heavyweight champion was ended by Britain’s Tyson Fury in 2015 before he failed to regain the IBF and WBA titles in the 11th-round defeat by Joshua.
Joshua produced a stunning seventh-round stoppage to beat Alexander Povetkin and retain his title in September.
However, he has yet to fight WBC heavyweight champion Deontay Wilder after discussions over a bout to unify all the belts fell through.
If the two do meet in the ring, Klitschko, 42, believes the result “could go either way”.
“Anthony Joshua is younger, he is definitely got talent, he’s heavier and he has heavy hands,” said the Ukrainian.
“Wilder is lighter. He has more experience in the professional boxing ring whereas Joshua is Olympic champion and has a great Olympic background, which Wilder doesn’t have.”