"It is with deep regret I announce that I will not be competing in the 2016 Summer Olympic Games this coming August in Rio de Janeiro," Day said in a statement.
"The reason for my decision is my concerns about the possible transmission of the Zika virus and the potential risks that it may present to my wife's future pregnancies and to future members of our family."
The 28-year-old was later joined by Ireland’s US Open runner-up Shane Lowry, ranked 25th in the world. Lowry, 29, who got married this year, said he felt he would be putting his future family plans at risk and based his decision on "firm medical advice".
Thus far, the likes of Northern Ireland duo Rory McIlroy and Graeme McDowell -- both down to compete for Ireland, Fiji's Vijay Singh, Marc Leishman of Australia and South Africa's Branden Grace in announcing their intentions not to compete at the Games.
The threat of the mosquito-borne virus, which can lead to birth defects, has been cited as the reason for withdrawal by a number of golfers, as the sport returns to the Olympics for the first time since 1904.
"I have always placed my family in front of everything else in my life," said Day, who has a four-year-old son Dash, and seven-month-old daughter Lucy.
"Medical experts have confirmed that while perhaps slight, a decision to compete in Rio absolutely comes with health risks to me and to my family.
"I will not place them at risk. I hope all golf and Olympics fans respect and understand my position."
The world’s number one golfer Jason Day, who won his first major tournament at the 2015 PGA Championship, has ten career titles including this year's Players Championship.
Lowry, who finished joint-second at the recent US Open, added he had "not taken the decision lightly and it has been a source of much anguish for me over the past week.
"I am a very proud Irishman and I love my country. Hence, I was really looking forward to walking out behind the Tricolour with the rest of the Irish Olympic team in Rio.
"While I am bitterly disappointed to be missing out on that experience and the opportunity to win an Olympic medal for Ireland, on this occasion I have to put my family's welfare first."
The World Health Organization's emergency committee on the disease has said there is a "very low risk" of the Zika virus spreading further internationally as a result of the Olympic Games in Brazil.
Is the Fear Validated?
Fears over the Zika virus is what’s driving most of the withdrawals. The virus has been the focus point of every golfer to date and it’s the reason almost every golfer gives now when announcing their decision. With so many unknowns still lingering over the disease, it’s hard to begrudge. However, one has to look at the fact that men are withdrawing from the event at a far higher rate than female golfers, which suggests there are more factors involved.
Even before Zika came into the public’s general consciousness, the inclusion of golf in the Olympics wreaked havoc on players’ schedule, particularly towards the latter part of the season.
Two majors — the British Open and the PGA Championship — and the Olympics will be contested in the five weeks between July 14th and August 14th. Two weeks later the four-tournament FedEx Cup playoffs begin, followed by the Ryder Cup immediately after. The threat of burnout lingers for players. For example, a top-ranked American or European golfer would find himself competing at least eight times over the course of just 13 weeks. No one plays that much. Do you a) take the leap of faith and make the grueling trip to Rio, or b) watch from the comfort of your own home and give yourself three weeks to prepare for the six week FedEx Cup-Ryder Cup stretch?
Lack of Excitement
Perhaps more than any other sport (outside of maybe baseball), golf is firmly entrenched in its traditions, and none more than the four major championships. Young golfers grow up thinking of little more than winning a major, which makes it hard for an outsider to break in.
It may be unjust to suggest that winning Olympic gold doesn’t measure up, but in reality, it simply doesn’t. Take Usain Bolt for example, this summer’s games most recognizable face. Four years of preparation will have been undertaken by the Jamaican, golfers’ highest priorities lie in the next Major on the horizon, or making a Ryder Cup team.
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