- Jordan Spieth missing from Olympic list
- Fellow American Dustin Johnson also out
- World's top four players to miss Rio
(CNN)Two-time major winner Jordan Spieth has become the latest top golfer to pull out of next month's Rio Olympics.
International Golf Federation president Peter Dawson confirmed Monday that the world No. 3 had withdrawn, citing concerns about the Zika virus.
Last month, Spieth, 22, said he was "uncertain" about taking part. Seen by many as the natural successor to Tiger Woods, his dazzling displays last year announced him as golf's brightest new star and propelled him to the top of the rankings.
Dawson was speaking at a news conference before this week's Open Championship in Scotland, where the game's leading players have assembled for the third major tournament of the golf season.
Spieth's decision means none of the world's top four will be involved when golf returns to the Summer Games for the first time since 1904.
The IGF released a list of 60 eligible men, which is led by world No. 5 Bubba Watson of the U.S. and includes only four of the world's top 10 players.
The women's list of 60, in comparison, features all the top 10. South Africa's 39th-ranked Lee-Anne Pace was the only female professional to say that she would withdraw ahead of Monday's announcement.
While the symptoms of Zika -- which include a rash, headaches and joint pain -- are not severe, the virus has been linked to microcephaly in newborn babies and some cases of the muscle-weakening disease Guillain-Barré syndrome in adults.
Last month, Brazil's new health minister told tourists and athletes that the risk of catching Zika in Rio was "almost zero."
"We are here to put at ease the minds of all residents and tourists coming to the games," Ricardo Barros said at a news conference.
He cited a study by Cambridge University that concluded there was a very low chance that any of the expected 500,000 foreign tourists would get the virus, which was detected in Brazil last year.
However, that has not assuaged the concerns of the world's leading golfers, many of whom have young families or are planning to start them.
World No. 1 Jason Day said last month he would not compete in Rio because of fears over Zika.
"The reason for my decision is my concerns about the possible transmission of the Zika virus and the potential risks it might present to my wife's future pregnancies and to future members of our family," the he explained.
"I have always placed my family in front of everything else in my life. Medical experts have confirmed that, while perhaps slight, a decision to compete in Rio absolutely comes with health risks to me and my family.
"While it has always been a major goal to compete in the Olympics on behalf of my country, playing golf cannot take precedent over the safety of our family. I will not place them at risk."
Second-ranked Dustin Johnson, the U.S. Open champion, did likewise Friday, while world No. 4 Rory McIlroy announced his decision not to play in June.
Other high-profile golfers to withdraw from the Rio Games include Adam Scott and Marc Leishman of Australia, South Africans Branden Grace, Louis Oosthuizen and Charl Schwartzel, Northern Ireland's Graeme McDowell and Fiji's former world No. 1 Vijay Singh -- most of whom have won major titles.
The U.S. team will be headed by Watson, world No. 7 Rickie Fowler, No. 13 Patrick Reed and No. 15 Matt Kuchar. Two-time Masters champion Watson cannot have children with his wife -- the couple have adopted a son and daughter.
The long line of withdrawals has raised questions about whether golf should be an Olympic sport.
Woods, arguably still golf's greatest draw despite the long-term back problems that have meant he cannot take part at Rio, said the Olympics "deserved" to have the best players involved.
The 14-time major winner said the qualifying format -- four players per country from the world's top 15, plus two players per country outside that -- also devalued the competition.
Dawson highlighted the impact golf's reintroduction has had on IGF membership, which has increased to a record 147 national federations from just over 100 in the eight years since the game was given a slot at Rio.
"The Olympic golf competitions will have a potential global audience of around 3.6 billion," the IGF said in a statement Monday, "representing the ultimate shop window for the sport and having the capacity to reach a brand new audience, especially among the younger generation across all the continents."
Next Monday, the IGF will announce a further 60 players each for the men's and women's competitions, which take place from August 11-14 and August 17-20 respectively at Reserva de Marapendi Golf Course.