(Reuters) — Late in July 2012, Phil Mickelson, one of the world's most famous golfers, received a phone call from a well-known professional sports gambler, William “Billy” Walters.

At the time, U.S. authorities say, Mr. Mickelson owed Mr. Walters a gambling debt, and Mr. Walters had a hot stock tip: buy shares in the food company Dean Foods Co.

Four days later, Mr. Mickelson owned $2.4 million worth of Dean Foods shares, according to the U.S. Securities and Exchange Commission. A few weeks after that, he reaped a $931,000 profit when the company announced a spinoff that sent its share price skyrocketing. Mr. Mickelson then paid off his debt to Mr. Walters.

On Thursday, U.S. authorities said Mr. Mickelson has agreed to turn over more than $1 million in profits and interest as part of an insider trading case brought against Mr. Walters and the former CEO of Dean Foods, Thomas Davis.

“Simply put, Mickelson made money that wasn't his to make,” Andrew Ceresney, the SEC's enforcement chief, said at a news conference in New York on Thursday.

Mr. Mickelson, 45, was named as a “relief defendant” in the SEC's civil lawsuit, a term for someone who is not accused of wrongdoing but has received ill-gotten gains as a result of others' illegal acts.

His lawyers said Mr. Mickelson was “an innocent bystander” and in a statement one of them said the golfer feels vindicated that he was not charged. He said Mr. Mickelson also takes full responsibility for “the decisions and associations that led him to becoming part of this investigation.”

It is unclear whether Mr. Mickelson benefited from an appellate court ruling in 2014 that limited the ability of authorities to bring insider trading charges against individuals who get inside information second or third hand, rather than directly from a corporate insider.

Gregory Morvillo, a New York lawyer who handles insider trading cases, said it was possible the ruling had a “chilling effect” on the SEC's authority to bring charges against Mr. Mickelson.

It remains to be seen whether the allegations will have an impact on Mr. Mickelson's reputation as one of the world's most popular golfers. His lawyer said the golfer appreciated that his corporate sponsors had decided to continue their agreements with him.

Sponsor is disappointed

Several of those sponsors, including golf club maker Callaway and pharmaceutical firm Amgen, did not immediately respond to Reuters' requests for comment. But the accounting firm KPMG said, “While we are disappointed by what the SEC announced today, we appreciate that Phil's statement makes clear he respects and shares the values of KPMG. We accept his statement of personal responsibility and commitment and have nothing further to add.”

Mr. Mickelson, who is ranked 17th on the PGA Tour this year, emerged as one of the world's top golfers in the mid-1990s and has won 42 tournaments.

For years he was known as “the best player never to win a major” tournament but he shed that label with a 2004 victory at the prestigious Masters. He has since won two other Masters titles and two other major tournaments.

Nicknamed “Lefty” and “Phil the Thrill,” Mr. Mickelson has long been one of golf's biggest draws and relishes interacting with fans along the course. While capable of driving up television ratings when in contention for the sport's bigger events, Mr. Mickelson also is admired for being a committed family man and a generous donor to charities.

The Professional Golfers Association website said Mr. Mickelson had career earnings of more than $79 million on the tour, second only to Tiger Woods' $110 million. In 2015, Forbes magazine estimated Mr. Mickelson earned more than $40 million a year from appearances and sponsorship deals, which also include Barclays P.L.C., Exxon Mobil Corp. and Rolex.

The SEC said Mr. Mickelson had placed bets with Mr. Walters both before and after July 2012, when the gambler called Mr. Mickelson with his Dean Foods tip. Messrs. Walters and Davis, the former Dean Foods CEO, had engaged in a years-long scheme to trade in the food company's stock ahead of major corporate announcements, according to federal authorities. Mr. Davis already has pleaded guilty.

The $2.4 million position that Mr. Mickelson took in Dean Foods using three brokerage accounts dwarfed his other investment holdings in those accounts, which together amounted to less than $250,000, the SEC said.

The Dean Foods case was brought by Preet Bharara, the U.S. attorney in Manhattan, who amassed a nearly perfect record in dozens of insider trading cases before the 2014 appellate court ruling limited the scope of insider trading laws.