Health concerns top medal pursuit for many ahead of Rio Olympics

Thousands of training hours. Multiple sacrifices. Maintaining a strict diet.

For much of the past four years, athletes from across the world have thrown themselves into the sport they love in hopes of realizing their Olympic dream in Rio de Janeiro in August.

But for some, health has taken precedence over athletic excellence in recent months following the Zika virus outbreak in Brazil. The mosquito-borne virus has been found to cause underdeveloped brains in babies born to women infected while pregnant and has been shown to cause extreme neurological birth defects and could induce neurological illnesses in adults.

The Olympics are not the pinnacle for most of the athletes who are choosing to skip Rio. For basketball and soccer, it's the respective league championships. In golf and tennis, it's the majors or the grand slams. A key point to note is that few athletes from the traditional Summer Games sports such as track and field or swimming have withdrawn from the Olympics.

Tennis star Rafael Nadal is baffled that players such as American John Isner, Australian Bernard Tomic and Feliciano Lopez have opted not to travel to Brazil.

"The experience of competing in an Olympic Games is completely different than any other event," Nadal told reporters in May. "If you don't want to be in the most important event in the world of sport, then [it] is difficult to understand what's the motivation for [other] things."

Below, we break down, by sport, the athletes who have pulled out of the Summer Games because of Zika concerns or other reasons, those pondering their Olympic future and some who have put aside their full-time sport to try to book their ticket for Rio in another.

Basketball

Steph Curry: The United States will try to defend its Olympic title without the two-time defending NBA MVP who says he will be rehabbing ankle and knee injuries during the Rio tournament after leading the Golden State Warriors to a league-record 73-win season. On Monday night, Curry and company will attempt to become the seventh team in NBA history to win back-to-back championships when they host Cleveland.

LeBron James: After six consecutive NBA Finals and seven in the past nine years, the Cavaliers' star forward told Cleveland.com he "could use a rest." James led the Cavs to a Game 7 win over Golden State to end a 52-year major sports championship drought in Cleveland.

Chris Paul: The Los Angeles Clippers' star point guard is skipping Rio to rest after fracturing a bone in his hand during this year's playoffs. Paul won Olympic gold medals with the U.S. in 2008 and 2012.

Anthony Davis: New Orleans Pelicans centre is staring at four to five months of recovery time following knee and shoulder surgery. He averaged 24.3 points and 10.3 rebounds per game this season.

Russell Westbrook: Oklahoma City Thunder guard didn't offer any specifics when announcing he was withdrawing from consideration for Rio. In 80 regular-season games in 2015-16, he averaged 23.5 points and 7.8 rebounds.

James Harden: Houston Rockets guard said he wouldn't play for the U.S. team in Rio, saying, "This decision was a painstaking one that I did not take lightly," but offered no further details.

Blake Griffin: The Los Angeles Clippers forward will be unavailable to Team USA after having a bone marrow procedure on his left quad tendon. Griffin averaged 21.4 points and 8.4 rebounds in 35 regular-season games.

Kobe Bryant: After telling reporters last November it would "mean the world to me" to play in Rio, the retired Los Angeles Lakers great changed his tune in January. Bryant won Olympic gold with the U.S. in 2008 and 2012.

Ben Simmons: The star forward and projected top-two pick at the 2016 draft on June 23 will not be available to the Australian Olympic squad because he wants to "concentrate fully on his NBA activities following the draft."

Cycling

Ryder Hesjedal: While the only Canadian to win a Grand Tour cycling race and the winner of the 2012 Giro d'Italia tweeted there's a "long season ahead," he didn't give a specific reason for withdrawing his name from Rio consideration. Hesjedal finished 28th in the individual time trial and 63rd in the road race at the 2012 London Olympics.

Tejay van Garderen: The 27-year-old would have been a likely choice for one of two spots on the U.S. team, but he feared contracting the Zika virus and passing it to his pregnant wife.

Golf

Jason Day: World No. 1 golfer will not be part of the 60-player field this summer in Rio because of concerns over the Zika virus.

Adam Scott: The 2013 Masters champion bowed out due to a "busy playing schedule" around the Rio Olympics and other commitments, both personal and professional.

Rory McIlroy: The 27-year-old has pulled out of Rio because of Zika concerns, saying he and his fiancee, Erica Stoll, may consider starting a family "in the next couple of years."

Louis Oosthuizen: In April, the South African said he was withdrawing from the Olympics because of family and scheduling issues.

Charl Schwartzel: He seemed a possibility to replace Oosthuizen on the South African team until he pulled out over Zika concerns.

Branden Grace: He joins fellow South Africans Oosthuizen and Schwartzel in withdrawing from Rio and became the fourth golfer to pull out due to the Zika virus. Married last November, Grace plans to start a family soon.

Marc Leishman: The 32-year-old Australian is concerned about Brazil's continuing health crisis. His wife, Audrey, developed toxic shock syndrome last year that nearly took her life.

Vijay Singh: The PGA Tour veteran informed Olympic officials in Fiji he would not participate because of "the Zika virus, you know and all that crap."

Miguel Angel Jimenez: Listed in April as the first alternate for Spain, he has withdrawn his name from the Olympic pool, but didn't publicly state his reason.

Soccer

Lionel Messi: The 28-year-old Barcelona star will be playing at the Copa America tournament in July instead of the Olympics in Rio since it had been agreed between his club team and Argentina that Messi would only play either of the two competitions. He won Olympic gold in 2008.​

Tennis

Dominic Thiem: Earlier this year, he told Austrian TV he considers Grand Slam events and Masters series tourneys to be more important in tennis than the Olympics, and instead will play a tournament in Los Cabos, Mexico.

John Isner: Considered the top American hope for a medal in men's singles, Isner opted to skip the Olympics to focus his efforts on the North American hard-court season.

Nick Kyrgios: Part of an Olympic uniform fitting session early in 2015, Kyrgios won't represent Australia in Rio after a dispute with its chef de mission, Kitty Chiller, who previously put Australia's top-ranked male player on watch and criticized his on-court behaviour.

Feliciano Lopez: The Spanish player prefers to focus on other events than the Olympics, with the Summer Games scheduled in the middle of the North American hard-court season leading up to the U.S. Open.

Bernard Tomic: He will not represent Australia, citing an extremely busy playing schedule and his own personal circumstances.

NFL careers on hold

Jarryd Hayne: San Francisco 49ers running back says he couldn't pass up the chance to compete with the Fiji rugby sevens in Rio. An undrafted free agent, the 28-year-old signed with San Francisco in March 2015 after giving up a lucrative rugby career in Australia.

Nate Ebner: New England Patriots special teams player took a leave from the NFL club earlier this year and was on the field in April in Singapore to represent the USA rugby sevens team.

David Wilson: The New York Giants' first-round pick in 2012 is attempting to qualify for Rio in triple jump after making his professional debut last summer. Wilson was forced to retire from football in August 2014 due to a serious neck injury.

Marquise Goodwin: The Buffalo Bills wide receiver/long jumper will compete for a spot on the U.S. Olympic team in July. A two-time NCAA long jump champion, he finished 10th at the 2012 London Olympics with a leap of 25 feet (7.8 metres).