Team Radioshack rider Lance Armstrong sits at the starting line in Visalia during the Amgen Tour of California in this May 20, 2010 file photo. [Photo/Agencies]

The legal team for cycling superstar Lance Armstrong, who is under federal investigation for doping, has asked a US judge to probe apparent leaks of secret grand jury proceedings examining the sport.

Armstrong, who won the Tour de France seven times, has denied taking banned substances but has had to fend off accusations by former teammates that he did so despite never failing drug tests.

The cyclist's newly hired legal team filed a motion in federal court in California asking a judge to investigate purported leaks from grand jury proceedings and require prosecutors to show why they should not be held in contempt.

"Each leak has revealed information damaging to Armstrong's reputation and has been carefully calculated to drum up publicity and cultivate public support for an investigation that is, to say the least, questionable in both its motive and its merits," his lawyers wrote in the 20-page motion filed last week and released on Monday.

A grand jury reviews possible wrongdoing and decides whether to issue an indictment based on evidence presented. The proceedings are mostly secret. Only witnesses who go before them may talk about what they said to the panel.

Armstrong in May hired two prominent defense lawyers, John Keker and Elliot Peters. They won a case for the Major League Baseball Players Association in which an appeals court ruled federal agents did not have the right to seize anonymous drug test results.

While they acknowledged prosecutors denied responsibility for the leaks, Armstrong's lawyers suggest a connection to the government, possibly an investigator who also was involved in the probe of anabolic steroids use in baseball, Jeff Novitzky.

"Something else that cannot be ignored is the fact that the leading government advocate for the Armstrong investigation, Novitzky, was recently connected to an investigation riddled with leaks to some of the same reporters involved in this case," the lawyers said.

They pointed to several news articles and reports about the grand jury probe into cycling and doping that cite unidentified people familiar with the investigation. They said the court could seek affidavits from investigators about media contacts.

Armstrong retired from cycling in February but has come under increasing scrutiny in recent months as former teammates have accused him of using performance-enhancing drugs. Cyclist Floyd Landis last year confessed to cheating and accused Armstrong of using performance-enhancing drugs.

US prosecutors have been investigating doping in sports for years, mostly focusing on Major League Baseball, but more recently have turned to cycling.

"The government has received the motion filed late last week and the government will file its opposition brief consistent with the briefing schedule that will be set by the district court," said Thom Mrozek, a spokesman for the US Attorney's office in Los Angeles.

He declined to comment on the allegations in the motion.