In August 2001, former professional cyclist George Mount was about to hop on his bike and embark on a leisurely ride in Northern California with his friend, three-time Tour de France winner Greg LeMond, when Mr. LeMond got a call on his mobile phone. It was Lance Armstrong, America's other legendary cyclist.

According to Mr. Mount, Mr. Armstrong had read comments Mr. LeMond had made about him in an article about doping allegations in the Guardian newspaper, where Mr. LeMond was quoted as saying he was "disappointed" with Mr. Armstrong's association with a controversial Italian doctor.

When Mr. Armstrong was done ripping into Mr. LeMond on the phone that day, Mr. Mount recalled, Mr. LeMond looked "like somebody had walked up and slapped him."

Former Tour de France winners Greg LeMond, left, and Lance Armstrong in 1999. Associated Press

That moment, now eight years past, proved to be the beginning of what has become one of the most enduring feuds in American sports -- one that has spawned personal attacks and a lawsuit. The battle between the two men has been playing out in federal district court in Minnesota, where Mr. LeMond is suing the bicycle maker Trek alleging breach of contract -- claiming, in part, that Mr. Armstrong was responsible for Trek's alleged neglect of Mr. LeMond's signature line of bikes.

Awaiting Mediation

Next week, Trek and Mr. LeMond go to mediation. If that fails, the case could go to trial next spring.

"I wish they'd all kiss and make up," says Mr. Mount, one of the pioneers of professional cycling in the U.S., who says he isn't in contact with Mr. LeMond or Mr. Armstrong and considers himself an impartial observer. "Guys are supposed to get over this stuff and move on with their lives."

The feud has divided cycling into two distinct camps -- those who support Mr. LeMond and those who support Mr. Armstrong. The fighting comes at a difficult time for the sport, which is still reeling from doping allegations and the departure of major sponsors and marketing dollars.

"When the biggest publicity the sport is getting is about doping accusations and former champions fighting current champions, it's not a good thing," says Mike Jacoubowsky, owner of Chain Reaction Bicycles in Northern California.

The Trek lawsuit, which was filed in the spring of last year, is essentially a contract dispute, but has been largely overshadowed by the feud. In court filings, Mr. LeMond levels some explosive charges, alleging that Mr. Armstrong paid off cycling officials to avoid positive drug tests and worked with a doctor known for his blood-doping expertise.

Mr. Armstrong says he has never used banned substances. The lawsuit also contends that Mr. Armstrong maliciously interfered with other LeMond business pursuits. Mr. LeMond declined to comment for this article.

Mr. LeMond argues that Trek neglected his brand of bikes at the behest of Mr. Armstrong as a way to get back at him for making disparaging comments about Mr. Armstrong in the media.

A representative for Trek says that even though it tried to get Mr. LeMond to stop bad-mouthing Mr. Armstrong, the company fulfilled its end of the contract. That left Trek caught in the middle of two of cycling's biggest names.

Ex-Wife Subpoenaed

The lawsuit's pre-trial discovery phase has widened recently, pulling in people closely related to Mr. Armstrong. Just last week Mr. LeMond's attorney subpoenaed Mr. Armstrong's ex-wife, Kristin Armstrong, to testify about a dinner at which, the suit alleges, Mr. Armstrong said he would get Trek to go after Mr. LeMond. Ms. Armstrong's attorney says she has no knowledge of the case. Her attorney has submitted a motion to keep her from being deposed.

In April, Mr. LeMond's lawyers accused Trek in court papers of organizing an anti-LeMond smear campaign with the help of Public Strategies Inc., a political consulting firm that has done work for high-profile political figures. Public Strategies also employs Mark McKinnon, who sits on the board of Mr. Armstrong's charity and has offices in the same building with Mr. Armstrong's handlers at Capital Sports and Entertainment in the San Jacinto Center in Austin, Texas. Trek says Mr. McKinnon did not work on the case. Mr. McKinnon and Public Strategies did not return calls for comment.

A Period of Cooling

The feud died down once Mr. Armstrong decided to retire after winning the 2005 Tour de France.

But last year, at a press conference at the Interbike trade show in September -- in which Mr. Armstrong was announcing an anti-doping program run by UCLA's Don Catlin -- Mr. LeMond showed up.

He called into question the testing procedures and offered his own method of testing. After more than five minutes of back-and-forth discussion, Mr. Armstrong said, "It's time for us, everybody in this room, to move on...I appreciate you being here -- next question."

Write to Reed Albergotti at reed.albergotti@wsj.com