Speaking to the BBC, a spokesman for the promoter said Lewis would be facing Klitschko in April in either Las Vegas or New York.
Should that fight take place it would put in doubt a bout between Lewis and Mike Tyson - which, according to reports, is scheduled for June 21 in Memphis.
The BBC quoted Universum Box-Promotion spokesman Rainer Koppke as saying: "I really believe in this fight.
"We don't have any problems with the deal or the fight.
"I don't think that Lennox Lewis is scared of Vitali, but I do think he wants more money.
"It's all just a question of money."
Certainly Lewis would pocket far more by setting up a re-match with Tyson than taking on Klitschko, the number-one rated contender for the belt.
"We might sue, or the WBC might decide that Lewis should retire if he doesn't want to fight the top contender," said Koppke.
Pay-per-view income for the first Lewis vs Tyson bout smashed previously records and a second would be expected to be another major money-spinner for HBO - Lewis' TV partner - and Showtime, which represents Tyson.
Some reports have said Lewis could earn an additional $15m by fighting Tyson.
The staging of sporting events is just one of the topics to be discussed at SportAccord, the leading industry conference taking place in Madrid between May 12-16.
To find out how YOU can attend, click on the link below to visit the official SportAccord website.
