Phil Mickelson had gambling losses of more than $US40 million from 2010-14, the author of an unauthorized biography on the golfer claims.
Author Alan Shipnuck's upcoming Mickelson book was the source of controversial remarks Mickelson made about Saudi financiers backing a rival golf circuit.
Shipnuck has released another excerpt of the book on line saying the gambling losses were uncovered by auditors during an insider trading investigation that Mickelson was involved in 2016.
"Mickelson's love of gambling is fundamental to understanding his style of play as a golfer. It might also explain the Saudi seduction," Shipnuck wrote.
"Based on his comments to me, he clearly enjoyed the idea of sticking it to the PGA Tour, but the real motivation was plainly the funny money being offered by the Saudis. Why was Phil so eager to cash in, at the risk of alienating so many fans and endorsement partners?
He then connected Mickelson's constant pursuit of money to his gambling issues.
The author noted that Mickelson's earning power at that point of his career helped him rake in an estimated $US40 million a year.
Mickelson received backlash for his remarks to Shipnuck admitting that the Saudis were "scary (expletives)" to deal with due to the nation's poor human rights record. He issued a lengthy mea culpa and retreated from the public eye, skipping the Masters.
Since then, Mickelson's representatives announced that the six-time major winner has registered for the PGA Championship (where he would be the defending champ) and U.S. Open, along with applying for a waiver to enter the first event of the LIV Golf Invitational Series.