Lennox Lewis has dismissed a possible fight against WBO heavyweight champion Wladimir Klitschko as a "waste of time."

Lewis, 36, has been considering retirement since knocking out Mike Tyson last month to retain his WBC and IBF titles.

Lewis said he had no interest in fighting Klitschko, a former Olympic gold-medalist from Ukraine, who retained his WBO version of the title on June 29 with a six-round win over 41-year-old Ray Mercer.

"Vladimir Klitschko -- he's not tough enough," Lewis said at a boxing ceremony in London. "It would be a waste of my time to go and fight him -- I would knock him out."

Lewis could be stripped of his IBF title next month if he does not sign to defend against No. 1 challenger Chris Byrd.

"I've already done everything that I really wanted to do in the sport of boxing," Lewis said. "But I'm going to keep them guessing for a little while longer."