Andy Murray shrugged off the potential threat of the Zika virus as well as the absence of two of his leading rivals on Tuesday as he prepared to defend his Olympic title.

The British star, who won his second Wimbledon crown last month, admitted he was just as likely to get bitten by mosquitoes, which carry the Zika disease, in Miami where he has a second home as he was in the sprawling Brazilian city.

However, he insisted that the absence from Rio of wife Kim and baby daughter Sophia was not related to the controversy which has seen a host of players refuse to come to Rio for health reasons.

"No, Kim and Sophia aren't coming. They were never coming," the 29-year-old said after his first training session at the Games.

"I spoke to my doctor and he assured me everything should be OK. Hopefully, I don't get too many mosquito bites, but I don't think it's too bad at this time of the year.

"There's a lot of places that are a little bit dodgy, like in Miami as well. You just hope that nothing happens."

Murray and world number one Novak Djokovic are the favourites to win gold in Rio.

And their paths to a potential final showdown on August 14 were cleared further on Tuesday when world number four Stan Wawrinka pulled out with a back injury.

Just last week, world number three Roger Federer also withdrew and shut down his season to recover from a knee injury.

"It's unfortunate with Roger and with Stan. They're obviously two guys who are great players and capable of winning at events like this, so it's a great shame they aren't here," said Murray.

"But still it's a pretty strong field. A lot of the top-20 players are here. It's unfortunate that a few of the top 10 are missing.

“Some of them are citing Zika as the reason, and there's a couple of injuries and that is unfortunate."