David Goldberg, who was married to Facebook’s second-in-command, is said to have slipped on a treadmill and hit his head.
The husband of one of Facebook’s most senior executives died after hitting his head when he fell off a treadmill, it is believed.
David Goldberg was exercising at a Mexican resort when he collapsed, an official familiar with what happened said.
He was on holiday with family and friends but it is not known whether his wife Sheryl Sandberg, Facebook’s chief operating officer and second-in-command to founder Mark Zuckerberg, was there.
The unnamed Mexican official said Mr Goldberg left his room in the Four Seasons Resort Punta Mita, near Puerto Vallarta, at about 4pm on Friday.
When the 47-year-old failed to return, family members went to look for him and found him at about 6.30pm in a gym.
He was lying in a pool of blood next to a treadmill, with an injury to the back of his head.
Mr Goldberg was showing signs of life, but he later died at a hospital in Nuevo Vallarta, the official said.
His official cause of death has been revealed as severe head trauma and hypovolemic shock, or bleeding.
Mr Goldberg ran online survey provider SurveyMonkey and had been married to Ms Sandberg, 45, since 2004.
The businessman had previously worked for the likes of Yahoo.
Ms Sandberg is worth an estimated $1bn but became famous beyond the tech world through her best-selling book Lean In, which aimed to show that women could reach the highest levels of corporate success while having a family.
She was named the ninth most powerful woman in the world by Forbes last year.
The Walt Disney Company delayed an announcement of its financial results to Tuesday morning to allow executives to attend Mr Goldberg’s funeral.