Johan Bruyneel, Lance Armstrong's team manager on the American's seven Tour de France wins, has left RadioShack Nissan after being implicated in his former protege's doping scandal.
The announcement on Friday comes as Tour de France organisers said they oppose re-attributing Armstrong's seven victories in the prestigious race.
"Acting in mutual agreement, on October 12 Leopard SA and Johan Bruyneel decided to end their collaboration. From this day on, Johan Bruyneel will no longer act in the position of General Manager of cycling team RadioShack Nissan Trek," a team statement read.
Bruyneel was named in the United States Anti-Doping Agency (USADA) report released this week which said he was one of the people who had helped Armstrong organise doping within the US Postal Team.
'No longer efficient'
"The reasoned decision published by the USADA included a number of testimonies as a result of their investigation. In light of these testimonies, both parties feel it is necessary to make this decision since Johan Bruyneel can no longer direct the team in an efficient and comfortable way."
Belgian Bruyneel was Armstrong's team manager when the Texan won his seven Tours from 1999-2005 as well as during his two Tour rides in 2009 and 2010 after his comeback from a 3-1/2 year retirement.
"The overwhelming evidence in this case is that Johan Bruyneel was intimately involved in all significant details of
the US Postal team's doping programme," the USADA report said.
A former professional rider, who finished seventh overall in the 1993 Tour de France, Bruyneel helped Armstrong to his seven Tour titles and Spaniard Alberto Contador to his two Tour wins in 2007 and 2009.
As a team manager, Bruyneel also won the Tour of Spain twice with Spain's Roberto Heras in 2003 and Contador in 2008, as well as the Giro d'Italia twice with Italian Paolo Savoldelli in 2005 and Contador in 2008.
Radioshack, the team launched by Armstrong in 2010, became RadioShack Nissan Trek this season after merging with Luxembourg owner Flavio Becca's Leopard Trek outfit.
Bruyneel owns large parts of the team's infrastructure through his management company.
The resignation comes as organisers of the world's most prestigious cycling race, the Tour de France, said they were against re-attributing Armstrong's seven victories.
The development came as the sport's world governing body said it was studying the extensive dossier on the Texan as a "priority", amid calls for its honorary president to quit and the possibility of legal action against three Spaniards implicated.
Armstrong, who has consistently denied taking banned substances, was this week placed at the heart of what the USADA called "the most sophisticated, professionalised and successful doping programme" ever seen in sport.
The organisation announced on August 23 that Armstrong was guilty of doping violations and recommended he was stripped of his career victories, raising questions about who would replace him at the top of the Tour podium between 1999 and 2005.
Tour director Christian Prudhomme said he was against re-allocating Armstrong's victories, describing the revelations contained in the USADA's 202-page "reasoned decision" and more than 1,000 pages of supporting testimony as "damning".
"What we want is that there is no winner," he said in his first comments on the report, calling the period a "lost decade" for the sport, which has been trying to clean up its act in recent years.
Prudhomme's statement comes even though the International Cycling Union (UCI) has not confirmed the USADA's findings but could head off further controversy.
Replacing Armstrong as Tour winner has been a source of debate since August, given that the majority of those who finished second or third -- and even lower down the field -- have subsequently been implicated in doping scandals.
Finding a rider untouched by links to performance-enhancing drug use would have been a difficult - if not impossible - task.
UCI president Pat McQuaid said it was still studying the USADA dossier against Armstrong.
"The legal department has been told that this is a priority, that we get the job done as quickly as possible and certainly within that time frame we will be back," he said on the sidelines of the Tour of Beijing.
The UCI -- under pressure to explain how drug cheats managed to avoid detection - has strenuously denied claims from a former team-mate of Armstrong that he donated money to cover-up a positive dope test in the 2001 Tour of Switzerland.