Walsh spoke to PRWeek last night after he gave a lecture titled "My fight with Lance Armstrong: lessons for journalism".
Asked how long it would take for the sport to be perceived as clean, Walsh said: "I don’t know how long, not in the next 10 years will it be perceived as clean. No, I think it will take a long time."
He stopped short of saying the current crop of Tour de France competitors were completely clean, but admitted it was a "cleaner" Tour.
"The recent winners of the Tour have been clean. I don’t think Bradley Wiggins is a doper, I don’t think Chris Froome is a doper. They won the last two Tours. There is no question it is a much cleaner, more credible race now."
He rejected criticism of this view from those who point to his employer's ownership of Froome and Wiggins' team sponsor Sky.
"Lots of people were critical of me, because I think these Team Sky guys are clean. Of course, people say ‘he works for Murdoch, Murdoch supports the team’. And I say ‘well, is that a reason I should tell a lie and say they are doping when I don’t believe they are doping?’"
Walsh also said he did not attach any blame to Armstrong’s PR advisers.
"They had a job to do. They were there to protect Lance, and I understood that," he said. "That didn’t mean they believed he was clean. They had a job to do."