Phil Mickelson asked legendary sports gambler Billy Walters to bet $400,000 for him on the U.S. team during a Ryder Cup competition in which he was playing, Walters claims in his new book — an allegation the golfer strongly denied.

The book also claimed Mickelson has gambled more than $1 billion on sports in the past 30 years, with some staggering figures attached.

Walters’ book, “Gambler: Secrets from a Life of Risk,” written with longtime investigative journalist Armen Keteyian, will be released on Aug. 22. The bombshell allegation is detailed in a book excerpt published on the golf site Fire Pit Collective.

“Have you lost your f–king mind?” Walters recalls asking Mickelson. “Don’t you remember what happened to Pete Rose?”

The former Cincinnati Reds manager was banned from baseball for betting on his own team.

“You’re seen as a modern-day Arnold Palmer,” Walters said. “You’d risk all that for this? I want no part of it.’’

Walters noted that he was unsure if Mickelson went through with the bet using another source.

Mickelson, after declining comment as he left Trump National Bedminster in New Jersey following a LIV Golf pro-am event, released a statement denying Walters’ Ryder Cup claim.

“I 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 said in a statement on Thursday.

“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. “

The alleged request came during the 2012 Ryder Cup in Medinah, Ill., which the U.S. lost after Europe overcame a 10-6 deficit on the final day. According to Walters, the request came several years into a partnership, in which Walters would supply Mickelson with sports betting plays, and Mickelson would place the bets.

As Walters described it, Mickelson’s reputation as a losing gambler enabled the golfer to have access to place large wagers with bookmakers, who would severely limit the size of Walters’ bets because he was a known winner.

“My reason for partnering with him was simple. Given my reputation in the gambling world, my limits with Phil’s two bookmakers were roughly $20,000 a game on college and $50,000 on the pros,” Walters wrote.

“Even after our fifty-fifty split, Phil’s limits of $400,000 on college at offshore sportsbooks and another $400,000 on the NFL enabled me to at least double my limits. Phil also had a $100,000 limit on college over/under bets with each book, twenty times my maximum.”

Walters also claims in the book some astounding figures on the size of Mickelson’s bets.

According to what Walters says are “detailed betting records and additional records provided by the sources,” between 2010-14 alone Mickelson bet $110,000 to win $100,000 more than 1,110 times, and $220,000 to win $200,000 nearly 900 times.

In all, those bets totaled more than $300 million. Meanwhile, just in 2011, Mickelson allegedly made more than 3,000 bets — an average of almost nine per day — and during one day in June of that year, lost $143,500 after making 43 bets on baseball games.

“Based on our relationship and what I’ve since learned from others, Phil’s gambling losses [between 2010 and 2014] approached not $40 million as has been previously reported, but much closer to $100 million,” Walters writes.

“In all, he wagered a total of more than $1 billion during the past three decades.”

In June, Mickelson claimed he has not gambled “in years” and that his net worth is approaching $1 billion.

Walters, who was convicted in 2017 of insider trading on the Dean Foods stock, says he believes that if Mickelson had testified a “simple truth,” that he would not have faced time in prison. Walters detailed his sense of betrayal in the book.

“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 wrote.

“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.

“The outcome cost me my freedom, tens of millions of dollars and a heartbreak I still struggle with daily. While I was in prison, my daughter committed suicide — I still believe I could have saved her if I’d been on the outside.”