By Mark Lamport-Stokes (Reuters) - Seven years after successfully pleading its case to be re-admitted to the Olympics following an absence of more than a century, golf is on increasingly shaky ground as it prepares to be showcased at the Rio Games next month. Three of the world's top-10 players in the men's game have already opted out of Rio, along with four other former major winners and exciting Japanese talent Hideki Matsuyama among others. Australian world number one Jason Day and fourth-ranked Rory McIlroy were vocal backers of Olympic golf until they decided not to go because of concerns over Zika, a mosquito-borne virus that is spreading across the Americas. More...