World number three Jordan Spieth has pulled out of next month's Olympics because of fears over the Zika virus, officials said at a news conference held at the British Open on Monday.
American Spieth's withdrawal means the Olympic golf tournament will be without the world's top four players.
Number one Jason Day, second-ranked Dustin Johnson and number four Rory McIlroy had all previously said they would not be competing in the event.
"It was out of concern at health issues we have been talking about (recently)," International Golf Federation vice-president Ty Votaw told reporters at Royal Troon, referring to the reasons for Spieth's pull-out.
Bubba Watson, Rickie Fowler, Patrick Reed and Matt Kuchar were also announced as the four players in the U.S. team for the Olympics in Rio de Janeiro.
Golf is returning to the Games in August following an absence of 112 years.
Zika is a mosquito-borne virus that the World Health Organisation says is spreading rapidly in the Americas.
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