Evander Holyfield has been given the chance to become a five-time world champion at the age of 44.
The American will face WBO heavyweight title holder Sultan Ibragimov in October after the Russian's scheduled opponent pulled out citing illness.
Ibragimov was set for a unification bout with current WBA champion Ruslan Chagaev of Uzbekistan.
"This is the first step on my quest to become the undisputed heavyweight champion of the world," said Holyfield.
"I'm glad Sultan Ibragimov was willing to give me a shot."
Holyfield is a former cruiserweight world champion who stepped up a weight to unify the heavyweight division.
He last fought for a world title when he was out-pointed by Chris Byrd in 2002.
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After losing a one-sided fight against Larry Donald in November 2004, Holyfield was suspended by the New York Athletic Commission on medical grounds.
After the ban was lifted, he returned to the ring last August and has won four bouts against journeyman opponents.
Having won the cruiserweight crown in 1986, Holyfield went on to dominate the heavyweight scene with wins over the likes of Michael Moorer, Riddick Bowe and Mike Tyson.
If he beats Ibragimov, he will become the second oldest heavyweight champion in history, behind George Foreman.
Ibragimov said: "Of course I am disappointed that Chagaev pulled out and won't allow me to unify our titles, but fighting a legend like Evander Holyfield is even better.
"And though I respect what he has done in his career, once the bell rings it will be all business, because he is trying to take what I have worked so hard for."
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