Phil Mickelson Wagered More Than $1 Billion on Sports Events, Gambler Billy Walters Claims in New Book

Mickelson denied Walters' claim that he once asked the gambler to place a $400,000 bet for him on Team USA in the 2012 Ryder Cup

A year after Phil Mickelson opened up about his “reckless” gambling addiction, a new book alleges the pro golfer has wagered more than $1 billion on sporting events over the last 30 years – including once attempting to place a $400,000 bet on his own team in the 2012 Ryder Cup.

In an excerpt from an upcoming book by famed professional gambler Billy Walters, it’s alleged Mickelson, 53, has placed thousands of bets between $100,000-$200,000 on football, basketball and baseball games over the years. In total, Walters estimates Mickelson lost roughly $100 million with the wagers.

“The only other person I know who surpassed that kind of volume is me,” Walters writes in his new book, Gambler: Secrets from a Life of Risk, according to NBC News.

Walters, a Las Vegas businessman who ESPN credits as perhaps the most accomplished American gambler of all time, will release the book later this month.

Related: Phil Mickelson Says He Lost 25 Lbs. Ahead of 2023 Masters: 'Getting My Speed and Strength Back'

Walters and Mickelson, once longtime friends, reportedly had a falling out during a federal investigation into stock trades they both made. Walters was convicted for insider trading in April 2017, according to The Washington Post, and blamed Mickelson for not testifying to defend him.

A spokesperson for Mickelson did not respond to PEOPLE’s request for comment on Walter’s book, though the golfer told Golf Digest on Thursday he “never bet on the Ryder Cup.”

“While it is well known that I always enjoy a friendly wager on the course, I would never undermine the integrity of the game,” Mickelson told the outlet.

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The allegations that Mickelson bet on a golf tournament he played in drew criticism and jokes from others around the golf community this week, including four-time major championship winner Rory McIlroy, who has often chirped back-and-forth with Mickelson in the press since the veteran golfer joined LIV Golf, a Saudi Arabian rival league to the PGA Tour, last year.

“At least he can bet on the Ryder Cup this year because he won't be a part of it," McIlroy said at a news conference Thursday.

Related: Who Is Phil Mickelson's Wife? All About Amy Mickelson

Mickelson first opened up about his gambling addiction in an interview with Sports Illustrated last year.

“My gambling got to a point of being reckless and embarrassing,” Mickelson said. “I had to address it. And I’ve been addressing it for a number of years. And for hundreds of hours of therapy. I feel good where I’m at there. My family and I are and have been financially secure for some time.”

Related: Golfer Rickie Fowler Buys Childhood Course Where His Dad Worked 'in Exchange for Me to Hit Balls'

He added: “Gambling has been part of my life ever since I can remember. But about a decade ago is when I would say it became reckless. It’s embarrassing. I don’t like that people know. The fact is I’ve been dealing with it for some time. Amy has been very supportive of it and with me and the process. We’re at place after many years where I feel comfortable with where that is. It isn’t a threat to me or my financial security. It was just a number of poor decisions.’’

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