(CNN) -- Dick Ebersol resigned Thursday as chairman of the NBC Sports Group after 22 years, a move that may put in doubt the network's broadcasting of future Olympic Games.
Ebersol spent a total of more than 40 years at NBC and more than two decades as head of the sports division, where he produced events ranging from Sunday Night Football and the Triple Crown to National Hockey League games and major golf and tennis events, NBC said.
His major achievement, however, has been overseeing NBC's coverage of the Olympic Games. After producing coverage of the 1992 Barcelona Olympics, he then secured the rights to broadcast every summer Games since, including next year's London Olympics.
Ebersol also acquired the broadcast rights to every winter Olympics since Salt Lake City in 2002.
Neither Ebersol nor NBC revealed what prompted his resignation, although The New York Times, which first reported the story, said Ebersol could not agree on a new contract with Comcast, which merged with NBC in January.
"What I have enjoyed most is working so closely with so many truly outstanding and incredibly talented people over decades of producing come of the greatest events in the world," Ebersol said in a statement released by NBC. "I simply want to say thank you to all of those people who have touched me so deeply throughout my career."
Mark Lazarus, who is currently president of the NBC Sports Cable Group and reported directly to Ebersol, will take over as chairman, the network said.
Ebersol's resignation comes a few weeks before the International Olympic Committee holds a meeting with U.S. networks to decide on broadcast rights for the 2014 and 2016 Games.
Along with NBC, both Fox Sports and ESPN are planning to bid for the rights at the meeting in Lausanne, Switzerland, June 6-7, spokesmen for the networks said.
Olympic rights expert Neal Pilson told Olympics news site Around the Rings that Ebersol's resignation "may impact the level of aggressiveness" with which Comcast approaches the Games.
Neither Fox Sports nor ESPN had any comment on Ebersol's resignation.
U.S. Olympic Committee Chairman Larry Probst said he was "extremely sorry" at the news, and USOC Chief Executive Scott Blackmun praised Ebersol's "transformative impact and unwavering passion" for covering the Games.
"Through his lens, he has told the moving stories of our athletes time and again, bringing them to life and sharing them with millions of fans," Blackmun said. "He leaves a legacy that will be nearly impossible to match -- one of leadership and conviction that will continue to benefit the Olympic movement for decades to come."
Lazarus is a former president of Turner Entertainment Group, where he oversaw all of the company's entertainment networks including TBS, Turner Network Television (TNT), Turner Classic Movies, and the Cartoon Network.
Before that, he was president of Turner Sports, overseeing all sports acquisitions, programming, and production. He acquired cable rights to the NBA, NASCAR, Wimbledon, and the British Open.