In "Wheelmen," a book by Wall Street Journal reporters Reed Albergotti and Vanessa O'Connell, the reporters claim the singer told feds about a time in which she saw her then-boyfriend get a blood transfusion on his private jet.
"He explained that it was simply part of the sport -- that all cyclists were doing the same thing," the book reads.
The writers add that Armstrong never thought Crow would share the information.
In 2011, federal agents reportedly offered Crow a deal to avoid prosecution by telling what she'd seen Armstrong do. According to the Washington Post, this was when Crow told authorities about the plane incident.
"Wheelmen" is due out Tuesday.