Phil Mickelson bet more than $1 billion on football, basketball and baseball over the past three decades and even allegedly attempted to place a $400,000 wager on Team USA in the 2012 Ryder Cup in which he participated, according to an upcoming book by renowned professional gambler Billy Walters.

Excerpts of the book "Gambler: Secrets from a Life of Risk" were first reported Thursday by Fire Pit Collective and provide the most detailed look yet at Mickelson's sports gambling and his relationship with Walters, a Las Vegas businessman who is widely considered to be the most successful American bettor ever.

Citing betting records and "two very reliable sources," Walters writes that from 2010 to 2014, Mickelson made 858 bets of $220,000 and 1,115 bets of $110,000. He estimates Mickelson endured losses of approximately $100 million while betting more than $1 billion over the past three decades.

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"The only other person I know who surpassed that kind of volume is me," Walters writes.

According to the book excerpts, in September 2012, Mickelson called Walters from Medinah Country Club during the 39th Ryder Cup and asked Walters to place a $400,000 wager for him on the U.S. team to win.

Walters responded by scolding Mickelson: "Have you lost your %&*$ing mind? Don't you remember what happened to Pete Rose? You're seen as the modern-day Arnold Palmer. You'd risk all that for this? I want no part of it."

Walters added that he didn't know whether Mickelson placed the bet elsewhere. The Americans lost the Ryder Cup to the Europeans by one point.

Mickelson denied ever betting on the Ryder Cup, saying later Thursday in a statement that he "would never undermine the integrity of the game."

"I never bet on the Ryder Cup," Mickelson said in his statement. "While it is well known that I always enjoy a friendly wager on the course, I would never undermine the integrity of the game. I have also been very open about my gambling addiction. I have previously conveyed my remorse, took responsibility, have gotten help, have been fully committed to therapy that has positively impacted me and I feel good about where I am now."

Mickelson's affinity and struggles with sports gambling have long been in the public domain. In 2015, court documents in a money laundering case revealed that nearly $3 million was transferred from Mickelson to an intermediary of "an illegal gambling operation." In 2021, The Detroit News revealed that Mickelson had been linked in court documents to an alleged mob bookie in a 2007 trial.

Mickelson was not charged in either case, but stories of his gambling have surfaced throughout his golf career, in which he has made more than $96.6 million in PGA Tour on-course earnings. The six-time major champion also reportedly signed a multiyear contract with LIV Golf worth about $200 million.

Phil Mickelson lost approximately $100 million during a three-decade stretch over which he wagered over $1 billion, according to an upcoming book by Billy Walters, who also alleged that Mickelson tried to wager on the 2012 Ryder Cup that he played in. Bob Donnan-USA TODAY Sports

In June 2022, he told Sports Illustrated that his gambling became "reckless," "embarrassing" and an "addiction." Two months ago, while responding to a question on social media about his gambling addiction, Mickelson said, "Haven't gambled in years. Almost a billionaire now. Thanks for asking."

Walters wrote: "Phil liked to gamble as much as anyone I've ever met. Frankly, given Phil's annual income and net worth at the time, I had no problems with his betting. And still don't. He's a big-time gambler, and big-time gamblers make big bets. It's his money to spend how he wants."

According to the book excerpts, Mickelson met Walters at the 2006 AT&T Pebble Beach Pro-Am. The two formed a betting partnership in 2008, which gave Walters access to offshore sportsbook accounts that Mickelson used to place big wagers. Because of Walters' betting success, bookmakers often refuse to take his action or limit the amount he can wager, so he partners with bettors who are offered larger limits.

"In all the decades I've worked with partners and beards, Phil had accounts as large as anyone I'd seen," Walters writes. "You don't get those accounts without betting millions of dollars."

Walters and Mickelson stopped their betting partnership in spring 2014, when it was revealed that federal authorities were looking into a series of stock trades they each had made. They had a falling-out after Mickelson refused to testify in an ensuing insider trading case against Walters. In April 2017, Walters was convicted on charges of conspiracy, securities fraud and wire fraud and was sentenced to five years in federal prison. His sentence was eventually commuted by then-President Donald Trump.

"Phil Mickelson, one of the most famous people in the world and a man I once considered a friend, refused to tell a simple truth that he shared with the FBI and could have kept me out of prison," Walters writes. "I never told him I had inside information about stocks and he knows it. All Phil had to do was publicly say it. He refused."

ESPN's Mark Schlabach contributed to this report.