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.
Senate Democrats to pull all-nighter on climate change
Teacher apologizes for showing sexual image of herself in class