Los Angeles: Tyler Hamilton, who recently went public with his claim that Lance Armstrong doped, had an awkward encounter with the seven-time Tour de France champion at a Colorado restaurant at the weekend, US media reported.
Hamilton was unnerved enough by the incident to inform his lawyers, who told the sports website they had formally notified US authorities of what they consider "aggressive contact" initiated by Armstrong.
Outside magazine first reported the chance meeting between the two at a restaurant in Aspen, Colorado, on Saturday.
Hamilton, who was in Aspen for an Outside magazine event, told a reporter from the magazine that Armstrong "wanted to get into it".
Armstrong, however, gave a different version, calling the meeting "awkward" but "truly uneventful".
Hamilton, 40, has testified before a federal grand jury probing doping in cycling.
He went public with doping allegations against Armstrong in an appearance on the CBS television news program "60 Minutes" last month.
Hamilton`s attorney Chris Manderson told the website that, according to his client, Armstrong berated him and asked him repeatedly how much he had been paid for the "60 Minutes" interview.
Armstrong has denied doping allegations, including those raised by former teammates and self-confessed dope cheats Floyd Landis and Hamilton, who claimed in the CBS report that Armstrong used EPO in preparing for the 2001 Tour de France.
Landis and Hamilton also claimed that the International Cycling Union (UCI) played a role in keeping a positive test at the 2001 Swiss race a secret.
Armstrong has demanded an apology from CBS over the report.
However, US investigators are looking into Armstrong as part of a probe into doping in cycling. Evidence of a positive drug test from Armstrong, who has denied ever testing positive for doping, could open the door for potential liabilities from fraudulent claims made to such former US cycling sponsors as the US Postal Service, which backed Armstrong`s racing squad for many years.
"Lance Armstrong is a possible defendant in an investigation that`s been widely reported, and Tyler is a probable witness," Manderson said. "When there`s any contact, especially aggressive contact, we as lawyers have a duty to inform the authorities... What they will do with it, I don`t know."