"Lennox has been discussing the prospect of a one-off, world title rematch with Vitali Klitschko," American promoter Bob Arum told the Daily Mail on Saturday.
"I am told Lennox is back in the gym. This is an enormous fight in the making."
Lewis retired three years ago. His last fight was a win over Klitschko in June 2003 when the Ukrainian was stopped after six rounds because of severe cuts.
The Briton became only the third man after Americans Gene Tunney and Rocky Marciano to retire while still world champion.
Klitschko announced last month that he was planning his own comeback.
"I am returning to get my WBC championship back," said the Ukrainian in a statement.
"In November 2005, due to a serious knee injury, I retired without having lost the WBC belt in the ring."
Klitschko's brother Vladimir is scheduled to defend his IBF and IBO heavyweight titles against American Ray Austin in Germany on March 10.