Evander Holyfield believes Anthony Joshua must take the opportunity to challenge Wladimir Klitschko sooner rather than later.
Joshua has blitzed his way through the heavyweight division since turning professional in 2013, a year after claiming gold for Great Britain at the 2012 Olympics in London.
The 25-year-old has won all 13 of his professional fights via knockout, with none of his opponents lasting past the third round against him.
Joshua faces unbeaten Scot Gary Cornish for the vacant Commonwealth heavyweight title at The O2 in London on Saturday, in what could well be his toughest fight to date.
However, Holyfield feels Joshua has already shown the credentials worthy of a world title contender and believes he must take a "risk" by challenging Klitschko even at this early stage of his professional career.
"Anthony Joshua is a great fighter. I got a chance to see him in the Olympics. He is a graceful big man," the former four-time world heavyweight champion said.
"I think you have to shoot for Klitschko, you have to shoot for one of the guys who is a champion. The only way to be a champion is to beat a champion. That's the risk you have to take.
"Anthony has great skills. He has the talent. He has the size and he just has to step up. You have to take the chance to be champion. If you never take the chance, you'll never get the chance to be champion.
"I think earlier is better. By him having not total professional experience, those fighters tend to get better than one who has fought for a long time. With his amateur background, I think he whips everybody out if he fights now."
Holyfield added: "His size and his strength, he can shift gears. One thing about the younger guy is that they can take it to the next level.
"The older guy settles down. If you wait later you can fall into the professional style and you can get outsmarted. He can out-hustle the guys if he fought them now."
Klitschko defends his IBF, WBO, IBO, & WBA (Super) titles against Tyson Fury on October 24 at Esprit Arena in Dusseldorf, Germany.
Fury, 27, has declared he will call time on his boxing career if he fails to beat the 39-year-old, whose last defeat came nearly 11 years ago against American Lamon Brewster.
Holyfield believes Fury will have to rely on his speed and reach if he is to stand any chance of becoming Britain's eighth world heavyweight champion.
"It's a very interesting fight because this is the first time Klitschko is fighting someone as big as him and with longer arms," the 52-year-old said.
"He will have to be a little bit more aggressive, otherwise the younger guy will have more speed and more energy and I think that may be the difference.
"Klitschko has got the experience, so if Tyson waits on him, Klitschko will out-box him. But if he uses his speed and reach it will be a great chance for him to win."