Phil Mickelson’s gambling losses were highlighted Thursday in an excerpt from a forthcoming biography.

While Mickelson was being investigated for his alleged role in an insider trading scheme, federal auditors discovered his gambling losses totaled more than $40 million from 2010 to 2014, according to the book excerpt from Alan Shipnuck.

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Phil Mickelson

Phil Mickelson tees off during Day 3 of the PIF Saudi International at Royal Greens Golf and Country Club Feb. 5, 2022, in Al Murooj, Saudi Arabia.  (Oisin Keniry/Getty Images)

The biographer wrote the auditors investigated "Lefty’s" finances over four years, from 2010 to 2014. The author cited a source with direct access to the documents. The golf star’s annual income in 2012 was estimated to be about $48 million. He netted about $1 million in one week from a Dean Foods stock deal.

The book also said Mickelson’s split with longtime caddie Jim Mackay in 2017 was largely about money and that Mickelson owed the caddie thousands of dollars in back pay.

Shipnuck also mentioned other wild expenses.

"Throw in all the other expenses of a big life — like an actual T. Rex skull for a birthday present — and that leaves, what, $10 million?" Shipnuck wrote, via The Firepit Collective. "Per the government audit, that’s roughly how much Mickelson averaged in annual gambling losses. (And we don’t know what we don’t know.) In other words, it’s quite possible he was barely breaking even, or maybe even in the red. And Mickelson’s income dropped considerably during his winless years from 2014 to ’17."

FLASHBACK: PHIL MICKELSON MAKES STARTLING COMMENTS ABOUT SAUDI GOLF LEAGUE: REPORT

Phil Mickelson

Phil Mickelson hits his tee shot on the fifth hole of the South Course at Torrey Pines during the first round of the Farmers Insurance Open golf tournament Jan. 26, 2022, in San Diego. (AP Photo/Denis Poroy)

"Phil: The Rip-Roaring (and Unauthorized!) Biography of Golf’s Most Colorful Superstar" is set to be released later this month.

Excerpts about Mickelson’s alleged leniency toward Saudi Arabia’s human rights abuses and the decision to join a Saudi-backed golf league also raised eyebrows.

Shipnuck posted a story based on a phone interview on "The Firepit Collective" website.

"They’re scary motherf-----s to get involved with," Mickelson reportedly said. "We know they killed [Washington Post reporter Jamal] Khashoggi and have a horrible record on human rights. They execute people over there for being gay. Knowing all of this, why would I even consider it? Because this is a once-in-a-lifetime opportunity to reshape how the PGA Tour operates.

"They’ve been able to get by with manipulative, coercive, strong-arm tactics because we, the players, had no recourse. As nice a guy as [PGA Tour commissioner Jay Monahan] comes across as, unless you have leverage, he won’t do what’s right. And the Saudi money has finally given us that leverage. I’m not sure I even want [the Saudi golf league] to succeed, but just the idea of it is allowing us to get things done with the [PGA] Tour."

Phil Mickelson

Phil Mickelson talks to the media during a practice round prior to the PIF Saudi International at Royal Greens Golf and Country Club Feb. 2, 2022, in Al Murooj, Saudi Arabia. (Luke Walker/WME IMG/WME IMG via Getty Images)

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Mickelson later apologized for those remarks.

The Associated Press contributed to this report.