LONDON (AFP) - Lennox Lewis has said he is prepared to fight one of the Klitschko brothers if they offer him US$100 million (S$125 million) - the biggest purse in boxing history.

It is nearly a decade since British boxer Lewis retired as the undisputed heavyweight champion of the world.

But such is the poor state of the division, the now 48-year-old Lewis said he was offered US$50 million in Moscow at the weekend while attending Wladimir Klitschko's successful defence of his world titles against Alexander Povetkin.

Lewis responded by promising to return to the ring for US$100 million.

The promoters are considering doubling their offer and the Briton told Thursday's Daily Mail: "That is my price tag and it is under discussion. I have told them I can be ready in six months and I am in provisional training."

Were Lewis to beat one of the Klitschkos, who between them hold all major versions of the world heavyweight title and have vowed never to box one another, he would surpass US boxing great George Foreman, who was 48 when he regained the world heavyweight title.

Foreman beat Michael Moorer in 1994 having first been crowned champion in 1973.

Lewis had previously talked of US$50 million being the required amount to make him contemplate a return to boxing.

"I said at the time that it will take US$50 million to get me out of my pyjamas but now I have to consider the value of my legacy of having retired as undisputed champion. That will cost them US$100 million," Lewis also told the Mail.

Lewis beat Vitali Klitschko on cuts in Los Angeles in 2003 and a year later retired without having boxed again.

The older of the Ukrainian brothers, the 42-year-old Vitali, who holds the WBC world title and harbours hopes of becoming President of Ukraine, has long wanted a return bout . Lewis, however, wants to fight Wladimir, 37.

"I beat Vitali so I would like to fight the other brother but we'll see how it works out. I want to bring back the Sweet Science to heavyweight boxing," he said.

Wladimir Klitschko retained his WBA, IBF, WBO and IBO titles with a unanimous points win over Russia's Povetkin in Moscow on Saturday.

He enjoyed an emphatic victory, putting Povetkin on the canvas five times, three times in the seventh round alone.

Lewis, however, was unimpressed.

"In a way this fight confirmed my disappointment with the state of heavyweight boxing right now. The best I could find to challenge Wladimir was a kid who is not fully developed either physically or in terms of experience.

"People paid a lot of money in expectation of a great fight but Povetkin was not properly prepared for the most important fight of his career.

"Wladimir should have gone for the knockout after putting him down four times but I think he missed having (the late) Manny Steward in his corner.

"Manny would have told him what he told me when I fought Vitali - to go in and finish him.

"But having said that he showed great movement, was very light on his feet and was never in danger of losing."

Lewis added he was prepared to put himself through a spartan training regime, having often prepared for big fights in the Poconos hills outside New York.

"I will go back to the mountains and into isolation. With the Russians involved I am thinking of training in Siberia."

Oscar de la Hoya was the highest-paid boxer, amassing US$53 million for his fight against Floyd Mayweather Jr in 2007, which he lost on a split decision. The money consisted of the guaranteed purse plus a percentage of the pay-per-view.

Lewis himself earned US$30 million in 2002, against Mike Tyson, whom he dominated and knocked out in the eighth round.