Top golfer Rory McIlroy has pulled out of this summer's Olympic Games in Rio de Janeiro due to fears over the Zika virus.
The Northern Irishman, 27, said "my health and my family's health comes before anything else" as he announced that he will not be travelling to Brazil.
Concerns about the Zika virus, which has been linked to birth defects and a rare autoimmune disorder in adults, have cast a shadow over Rio 2016 but the International Olympic Committee, with guidance from the World Health Organisation (WHO), has resisted calls for the Games to be moved or postponed.
On Tuesday the WHO issued health guidance which doctors should circulate to their patients who are planning to travel to the Games.
The majority of those infected with Zika will have no symptoms, while for others it can cause a mild illness, with symptoms including a rash, fever and headache.
But the virus has been linked to serious neurological disorders among babies born to women infected while pregnant. Officials have also noted a number of cases of a rare but serious form of muscle weakness, called Guillain-Barré Syndrome, among adults.
The virus is mostly spread through mosquito bites but cases of transmission through sexual contact have also been noted.
The WHO advice tells doctors to warn their patients about the risk of becoming infected, urge them to protect themselves against mosquito bites and have safe sex.
Pregnant women are advised not to travel to areas where there are ongoing outbreaks, including Brazil.
The guidance also states that doctors should warn pregnant women whose partners live in or travel to areas with Zika virus outbreaks to ensure safe sexual practices or abstain from sex for the duration of their pregnancy.
Travellers should be advised to practice safe sex or abstain from sex during their stay in Brazil and for at least eight weeks after their return.
And if men experience symptoms of the Zika virus they should adopt safer sex practices or abstain from sex for at least six months, WHO said.
Meanwhile, there are measures in place to prevent people who are potentially infected from donating blood for a period after their return to the UK.
McIlroy, the world number four, is one of a string of high-profile golfers to pull out of the Games, with Adam Scott, Louis Oosthuizen, Charl Schwartzel, Marc Leishman and Vijay Singh having already said they will not travel to Brazil.
McIlroy said in a statement: "After much thought and deliberation, I have decided to withdraw my name from consideration for this summer's Olympic Games in Rio de Janeiro.
"After speaking with those closest to me, I've come to realise that my health and my family's health comes before anything else.
"Even though the risk of infection from the Zika virus is considered low, it is a risk nonetheless and a risk I am unwilling to take.
"I trust the Irish people will understand my decision. The unwavering support I receive every time I compete in a golf tournament at home or abroad means the world to me.
"I will continue to endeavour to make my fans and fans of golf proud with my play on the course and my actions off it."
In February, WHO said that Zika's links to microcephaly and other neurological disorders should be considered a "public health emergency of international concern".
Sixty countries and territories are reporting "continuing mosquito-borne transmission", WHO said.
The mosquitoes which carry the virus are not found in the UK but since the start of the current outbreak, a total of 27 cases have been diagnosed in UK travellers who have been to affected areas.
Jonathan Ball, professor of molecular virology at the University of Nottingham, said: "Obviously I don't know the reasons for this decision, but it does strike me as being extreme.
"The chances of being infected by the Zika virus is low, especially if you protect yourself from mosquito bites by covering up and using a good insect repellent.
"Pregnant women are advised not to travel to an affected area, and couples planning to have children in the very near future should also consider how the risk of Zika infection may affect their plans. But we must remember that most people infected don't even show any symptoms and serious illness, although reported, seems to be a very rare event."
Dr Derek Gatherer, lecturer in the Biomedical and Life Sciences department at Lancaster University, said: "Zika is a risk to pregnant women and to men and women who are planning pregnancy.
"Another, much smaller, risk group is those who have had previous attacks of Guillain-Barre Syndrome or who have been told by their doctors that they are at risk of GBS.
"If Mr McIlroy is contemplating becoming a father within a year or so, then it is a perfectly reasonable precaution to stay away from regions of active Zika transmission. On the other hand, if he is not going to become a father any time soon, he has little to worry about, provided he takes the usual precautions for tropical countries, which for Brazil now includes no unprotected sex for at least eight weeks after returning even for men who experience no symptoms."
Jimmy Whitworth, professor of international public health at the London School of Hygiene & Tropical Medicine, said: "Rory Mcllroy has made a personal decision not to attend the Rio Olympics. That is as it should be, we do not know his personal circumstances and we should respect his decision.
"Golf courses would not be particularly dangerous places for getting infected with Zika. The mosquitoes involved in transmitting the infection live around houses and rarely fly more than 50 metres from the breeding sites."