"Lance was going to be running as a fundraising team member of Team Livestrong at Chicago," Mark Higgins told Reuters. "One of the Lance Armstrong Foundation staffers had communicated that to the race organisers and she was told he could not run."
Armstrong was stripped of his record seven Tour de France wins last month and handed a lifetime ban by the United States Anti-Doping Agency after indicating that would not challenge charges that he had doped throughout his career.
Armstrong, whose Livestrong Foundation has raised hundreds of millions of dollars in the fight against cancer, has always denied doping.
"When he chose not to contest in a public hearing the overwhelming evidence of his cheating Mr. Armstrong was well aware that he was accepting ineligibility from world-class athletic events like the Chicago Marathon," a USADA spokeswoman said in a statement.
"This is what the world rules require for all sanctioned athletes, high profile or not."
A marathon spokeswoman said Armstrong had not submitted a formal registration to participate in the October 7 marathon, but that the race follows rules that prohibit banned athletes from entering races sanctioned by USA Track & Field.
- Livestrong Foundation