The British Broadcasting Corp. reported that the challenge in Los Angeles was stopped by ringside doctor Paul Wallace after the Ukrainian got a deep cut above his left eye.
"I'm really disappointed that the doctor stopped the fight," Klitschko told Radio Five Live's Sportsweek Program. He added, "I was ready to continue, and I am sure I would have won."
Klitschko was ahead on points when the match was stopped after the sixth round, the BBC reported.
American promoter Gary Shaw, speaking on Sportsweek, said a second fight could happen "if the money is right."
Shaw also said that Lewis might choose to meet Roy Jones Jr., who took John Ruiz's WBA heavyweight title.