The U.S. Justice Department will notify a federal court Friday of its plans to become a co-plaintiff in a lawsuit filed against American former road cyclist Lance Armstrong by an ex-teammate, NBC News reported, citing legal sources.

The government is signing on to a suit that American former cyclist Floyd Landis, an admitted PED user, filed two years ago against Armstrong over the latter's use of performance-enhancing drugs during the Tour de France, the sources said.

They told NBC the Justice Department is joining the case on the grounds that Armstrong defrauded the government by violating its strict rules against illegal drugs while racing for the U.S. Postal Service team.

NBC, however, cited legal experts as saying Armstrong could argue that his contract with the team - of which he was a member from 1998-2005 - did not explicitly prohibit blood doping, and that he never signed any agreement directly with the Postal Service banning PED use.

The athlete had denied cheating for a decade, but he told Oprah Winfrey last month that he took banned substances and received blood transfusions throughout most of his racing career and during all the Tour de France races he won.

Prior to that admission, Armstrong had been stripped of his seven consecutive Tour de France titles between 1999 and 2005 after refusing last year to defend himself from doping allegations compiled by the U.S. Anti-Doping Agency.

He told Winfrey in an interview aired on her OWN network that, in his opinion, it would have been impossible to win the Tour de France over that seven-year period without the aid of banned substances.

In issuing a 1,000-page report last October detailing Armstrong's involvement in a "doping conspiracy," USADA said the U.S. Postal Team "ran the most sophisticated, professionalized and successful doping program that sport has ever seen." EFE