Andy Murray of Great Britain practices at the Olympic Tennis Center in Rio de Janeiro, Brazil, 02 August 2016. The Rio 2016 Olympic Games take place from 05 to 21 August. EPA/ERIK S. LESSER

Spanish tennis player Garbine Muguruza during a training session prior the Rio 2016 Olympic Games Tennis events in Rio de Janeiro, Brazil, 03 August 2016. EPA/LEONARDO MUNOZ

Sam Groth of Australia serves during a practice session for the Rio 2016 Olympic Games Tennis events at the Olympic Tennis Centre in the Olympic Park in Rio de Janeiro, Brazil, 05 August 2016. EPA/SAM MOOY

Australian Tennis player Daria Gavrilova in action during a training session for the Rio 2016 Olympic Games Tennis tournament in Rio de Janeiro, Brazil, 05 August 2016. EPA/SAM MOOY

Serena Williams of the US stretches while taking a break during practice with her sister Venus Williams (not pictured) at the Olympic Tennis Center in Rio de Janeiro, Brazil, 03 August 2016. The Rio 2016 Olympic Games take place from 05 to 21 August. EPA/MICHAEL REYNOLDS

Rafael Nadal of Spain serves during a practice session for the Rio 2016 Olympic Games Tennis events at the centre court of the Olympic Tennis Centre in the Olympic Park in Rio de Janeiro, Brazil, 05 August 2016. EPA/SAM MOOY