"We are grateful for Scott's years of service and his many contributions to the company, and wish him the very best of luck as he moves forward," the statement said. "We are fortunate to have a talented team in place at MSG Sports who will continue to build on the company's successes while we undertake a search for a new president of MSG Sports."
Under O'Neil, who joined the Garden in 2008, the Rangers made the playoffs three times, including last season, when they lost in the Eastern Conference finals to the Devils. The Knicks have been in the postseason each of the past two seasons.
"I am thankful and extremely proud of what we accomplished at MSG Sports," O'Neil said in a statement.
"There is nothing more rewarding than the opportunity to help build a world-class staff and seeing them perform beyond our loftiest expectations -- people I consider not only the most talented in the business, but also true friends. To help lead and steward iconic brands like the Knicks and Rangers and sell the transformed Garden in a city like New York has been a true privilege."