Armstrong was stripped of his seven titles in 2012 for doping offences, leaving LeMond, who won the yellow jersey in 1986, 1989 and 1990, as the only American victor of the race.
The 52-year-old believes that, should the playing field have been level when Armstrong was riding, then the infamous drug cheat would not have been close to competing for major honours.
"If he was clean and everybody else was clean, he's a top-30 [Tour finisher] at best," LeMond told CNN.
"He's not capable of winning the Tour, he's not capable of the top five."
Armstrong, 42, has been banned from cycling for life following a United States Anti-Doping Agency investigation.