Marion Jones admitted using steroids before the 2000 Olympics in a recent letter to close family and friends, The Washington Post reported Thursday.
Jones, a triple gold medalist in Sydney, said she took "the clear" for two years, beginning in 1999, and that she got it from former coach Trevor Graham, the newspaper reported. Graham told her it was flaxseed oil.
"The clear" is a performance-enhancing drug linked to BALCO, the lab at the center of the steroids scandal in professional sports.
Jones had steadfastly denied she ever took any kind of performance-enhancing drugs.
Jones is scheduled to appear in U.S. District Court in White Plains, N.Y., on Friday to plead guilty to charges in connection with her steroid use, a federal law enforcement source told The Associated Press. The official spoke on condition of anonymity because the investigation is ongoing, and would not provide specific details about the plea.
"I want to apologize for all of this," the Post reported Jones saying in her letter, quoting a person who received a copy and read it to the paper. "I am sorry for disappointing you all in so many ways."
Jones said in her letter that she faced up to six months in jail and would be sentenced in three months, according to the newspaper.
"Red flags should have been raised when he told me not to tell anyone," the Post reported, quoting the letter.
No one answered the door at Jones' Austin, Texas, home Thursday night, and a message left by the AP for a phone number registered to her husband, Obadele Thompson, was not immediately returned.
The admission could cost Jones the five medals she won at the Sydney Olympics. Though she fell short of her goal of winning five gold medals, she came away with three and two bronzes and was one of the Games' biggest stars.
But her career has been tarnished by doping allegations since then. Victor Conte, head of the Bay Area Laboratory Co-Operative, repeatedly has accused Jones of doping.
Speaking to ESPN.com's Mike Fish on Thursday, Conte reiterated his claim that Jones cheated her way to Olympic success by using the oil known as "the cream" and arthritis balm commonly called "the clear."
"What I said in December of 2004 is that Marion Jones had used the cream and the clear -- that was a true statement," he said. "I'm here today saying the same thing again -- that before during and after the Olympic Games in 2000 that Marion Jones used [performance-enhancing drugs]."
Jones sued Conte in 2004 for $25 million after he told a national television news program that the sprinter used designer steroids, human growth hormone and other illegal performance enhancers before and during the 2000 Summer Olympics in Sydney.
Conte said he taught Jones how to inject human growth hormone during a track meet in 2001. He said he also held conference calls with Jones and Graham where the three of them discussed Jones' "doping" regimen.
"Jones has never taken banned performance enhancing drugs," the sprinter alleged in her defamation lawsuit. "Jones took and passed over 160 separate drug tests, including five different drug tests at the 2000 Olympics."
The pair settled the lawsuit in 2005 for an undisclosed amount.
Jones was one of several athletes, including home run king Barry Bonds, New York Yankees slugger Jason Giambi and Detroit Tigers outfielder Gary Sheffield, to be linked to BALCO and were among more than two dozen athletes who testified before a federal grand jury in 2003.