Jordan Spieth & Rory McIlroy on Rio 2016 Olympics

Jordan Spieth says golf has a place at the Olympics, and he wants to play in Tokyo in 2020

American Jordan Spieth says withdrawing from the Olympics was the "hardest decision I've had to make in my life".

The world number three cited "health concerns" for his decision but did not refer specifically to the Zika virus, as have Jason Day and Rory McIlroy.

Spieth, 22, added: "Do I think it looks bad on golf? Maybe."

But Northern Ireland's McIlroy was less apologetic, saying he may watch "track and field, swimming, diving, the stuff that matters" but perhaps not the golf.

Spieth's decision to pull out, announced on Monday, means none of the world's top four will be in Rio this summer, following the withdrawals of Day, McIlroy - who was set to represent Ireland - and world number two Dustin Johnson.

But the two-time major winner said: "I'm making the decision that's best for me but I don't feel like I have to carry the torch for the sport.

"I do hope to play in four or five Olympics in the future, but it's unique circumstances this year.

"It was harder than deciding what university to go to or whether to turn pro.

"Why was it so hard? I'm a huge believer in Olympic golf and playing for your country."

McIlroy, 27, who has four majors, was the first of the top four to withdraw from the Games, saying that golf's majors were more important to players than winning a gold medal.

And speaking ahead of Thursday's Open at Royal Troon, he added: "I have no regrets about it at all.

"I'll probably watch the Olympics, but I'm not sure golf will be one of the events I'll watch.

"I don't feel like I've let the game down at all. I didn't get into golf to try to grow the game, I tried to get into golf to win championships."

• Zika Olympic risk low says WHO

• Zika virus - special report

Zika has been found to cause Guillain-Barre, a rare neurological syndrome that causes temporary paralysis in adults.

Carried by mosquitoes, the virus has also been linked to thousands of babies being born with underdeveloped brains.

Masters champion Danny Willett, who will be ranked fourth in Rio, said there is "more chance of getting Malaria in South Africa than Zika in Rio".

"Would people pull out if the Olympic Games were in Johannesburg? I don't know," said the Englishman.

All four top male players have withdrawn - but just one female golfer has pulled out owing to health concerns

Golf is back in the Olympics after a 112-year absence, but the withdrawal of the top male players has overshadowed its return.

"I sympathise with them," added Justin Rose, who will now be ranked fifth when he represents Team GB in Rio.

"But from my point of view I see it as a once in a lifetime opportunity and it's about being part of something bigger than your sport.

"The Olympics is about the best of the best going head to head no matter what the sport, so golf has been hit quite hard in that respect."

Meanwhile two-time Ryder Cup winner Francesco Molinari has withdrawn from Italy's Olympic team, citing "family reasons".