He made the announcement in a prepared statement, released through a public relations firm. He informed the Knicks with a fax, apparently catching them by surprise.
Contacted by the Associated Press for a comment, a Knick spokesman refused to confirm or deny the report, saying, "If and when we have anything to say, we'll say it."
The Knicks then hastily called a news conference at which team President Dave Checketts, the man who hired Riley and a steadfast ally for their four years together, rebutted everything Riley had said.
Riley, 50, who had been offered a five-year, $15-million extension, said in his release he needed control of personnel matters.
At the news conference, Checketts noted that Riley had asked for a share of ownership too.
"If anything, he was resentful I couldn't deliver to him ownership and everything he was seeking," Checketts said. "We delivered an offer to him that we thought was extraordinary."
Newsday reported that Riley at one point asked for $50 million over five years, plus 25% ownership of the team, and the Knicks countered with a five-year, $25-million offer.
The Knicks and Madison Square Garden were recently purchased by ITT, a multinational corporation, which won an intense competition with several other multinationals and had no intention of giving away even a piece of its prize.
In his release, Riley said his decision "had absolutely nothing to do with money" but everything to do with power.
"For the last two years," Riley said, "I had consistently and repeatedly expressed to Knick management my desire and need to be charged with ultimate responsibility for all significant aspects of the ballclub. During this time, I had tried my best to reach an agreement with management on these issues. Unhappily, the gap between us could not be bridged."
Riley's departure was surprising, only because he had recently suggested he would return, insisting the Knicks weren't too old and used up but had been hurt by internal divisions.
Said Riley shortly after the Knicks were ousted by the Indiana Pacers in Game 7 at Madison Square Garden: "We had a team that was good enough to win. It was built to win. . . . But we should have been on the upswing this year as a team that was totally together. For the majority of the season, we were pulling apart."
However, the Knicks also had tangible problems.
For the first time since Riley took over a 39-43 team in 1991, they had gone backward. In his first three seasons, they had gone from 51 victories to 60 to Game 7 of last spring's NBA finals. But this season, with 32-year-old Patrick Ewing and 31-year-old Charles Oakley hobbled by injuries, they sagged to second in the Atlantic Division--the first time in 13 seasons a Riley-coached team had not finished first--and were eliminated in the second round of the playoffs.
Moreover, there were signs this was like his last season with the Lakers, when the players grew tired of him and vice versa.
The season was filled with turmoil, Riley at one point charging his players were "unprofessional." In another crisis, Riley suspended rebellious Anthony Mason, was booed by the Garden crowd that once cheered his every gesture, and even offended the faithful Ewing, who appeared to side with Mason.
Nor will rebuilding be easy. Ewing gets a salary cap-busting $18-million balloon payment next season. There is little demand for any of the Knicks' other players.
Perhaps weighing his options, Riley had left the Knicks' $3-million-a-year offer on the table all season (he was already basketball's best-paid coach with salary and perks worth nearly $2 million a season).
"During the past two years, there has been an uncertainty over whether or not Pat Riley wanted to remain with the Knicks," Checketts said. "We had offered him a financial package that was unprecedented in any sport. However, we never came close to his financial demands."
The Knicks say they want a pro coach. Hoping to land another big name fast, they're eyeing former Detroit Coach Chuck Daly, a proven winner but 64 years old. Behind him are Don Nelson, currently unemployed, and Cleveland Coach Mike Fratello, reportedly at odds with his front office.
The Knicks reportedly will not let Riley work next season, the last on his contract. However, there are no Riley-type teams out there, close to winning a championship, and after a season he called the hardest in his career, he can use a rest.
After what they've put him through, he's earned it and vice versa.
* Times staff writer Chris Baker contributed to this story.