#5 John Isner (USA)
John Isner is only one of the few tennis stars who will be skipping the Rio Olympics. Players such as Roger Federer, Rafael Nadal, Andy Murray, will all be in Rio to aim for glory. But the American has cited his logistics and scheduling as the main reason why he won't be able to represent his nation at the Games.
The American player is currently ranked number 16 in the world and would have been the top ranked USA player in tennis. But now it will be world number 26, Jack Sock, who will be the highest ranked tennis player from USA at the Games.
Isner had participated at the 2012 London Olympics and was beaten by Roger Federer in the quarterfinals. Isner also added that he would also like to rest his body during August as tournaments such as the Western & Southern Open Masters event in Cincinnati and then the US Open will take place.
He said he needs to be fresh for those tournaments in order to perform well in them.