Leopard SA - the company behind the RadioShack-Nissan team - said the decision was taken by "mutual agreement," adding that Bruyneel is no longer able to direct the team in what it refers to as "an efficient and comfortable way."

"His departure is desirable to ensure the serenity and cohesiveness within the team," it said in a statement.

Bruyneel said he was leaving "to concentrate on my defense," having opted for an arbitration hearing to fight charges leveled by the U.S. Anti-Doping Agency.

Armstrong was banned from Olympic sports for life by USADA and stripped of his seven Tour titles after choosing in August not to contest the allegations, including that he used and supplied banned drugs.

Friday's announcement came two days after USADA's damning report on Armstrong exposed the doping program in the U.S. Postal Service and Discovery Channel teams that Bruyneel managed when Armstrong rode to seven straight Tour de France victories from 1999-2005.

"In light of these testimonies, both parties feel it is necessary to make this decision," RadioShack said. Its sponsors include longtime Armstrong backers Nike, Trek, Oakley and Livestrong.

Bruyneel, who was general manager of the Luxembourg-based team, now has his own legal battle with USADA which placed him at the heart of doping programs for Armstrong's teams through the rider's second retirement in 2010.

"I am surprised and extremely disappointed that USADA released information in the public domain relating to their pending case against me before I had been given any opportunity to review the evidence and provide my defense against it," Bruyneel said.

"I still hope to be able to defend myself in a forum free from bias, although I now fear that USADA's calculated action may have irreversibly prejudiced my case," he said in a statement published on his personal website.

Armstrong and Bruyneel were an unbreakable partnership for years, with Armstrong widely crediting the Belgian for helping him achieve his Tour successes on a U.S. Postal Service team that dominated cycling's showcase race.

Armstrong rode his final Tour in 2010 under Bruyneel's leadership, with the new RadioShack team that Armstrong co-owned. Bruyneel also helped Spaniard Alberto Contador win the 2007 Tour for the Discovery team and worked with both Armstrong and Contador on the 2009 Tour, which Contador also won.

USADA's dossier pinpointed Bruyneel as the focal point of massive doping throughout the USPS team's heyday.

"The overwhelming evidence in this case is that Johan Bruyneel was intimately involved in all significant details of the U.S. Postal team's doping program," USADA said in its 200-page report. "He was on top of the details for organizing blood transfusion programs before the major Tours, and he knew when athletes needed to take EPO to regenerate their blood supply after extracting blood."

The report added that "Bruyneel learned how to introduce young men to performance enhancing drugs, becoming adept at leading them down the path from newly minted professional rider to veteran drug user."

Former Armstrong teammates also said Bruyneel appeared to have advance knowledge of when drug-testing teams would arrive to take samples.

Team RadioShack-Nissan's parent company Leopard SA, which is backed financially by Luxembourg entrepeneur Flavio Becca, thanked Bruyneel for "his dedication and devotion" to the team, but was quick to further distance itself from him.

"The USADA investigation does not concern the activities of Mr. Bruyneel while managing," the team, the statement said.

At this year's Tour de France, RadioShack-Nissan team leader Frank Schleck tested positive for a banned diuretic.

The Luxembourg rider was pulled from the Tour de France after the International Cycling Union (UCI) said he had tested positive for the banned diuretic Xipamide. Schleck has a disciplinary hearing scheduled with the Luxembourg cycling federation on Monday.

Tensions within the RadioShack-Nissan team were detailed in comments by star rider and former World Champion Fabian Cancellara reported earlier today by Belgian daily Het Laaste Nieuws.

"I've heard that in 200 pages, Bruyneel's name appears 129 times," the Swiss rider said. "I want to know what happened. I don't know if I can work with Johan."

Teammate Jens Voigt earlier today was quick to refuse being engaged in any doping-related activities. On Twitter Voigt wrote "You ask if i doped? Ok here is the answer. No i did not dope in the past, i don't do it now and not planning it in the future."