Spain’s Rafael Nadal returns the ball to Switzerland’s Stanislas Wawrinka during their singles Ilie Nastase group match of the ATP World Tour Finals tennis tournament at the O2 Arena in London, Britain, 16 November 2015. EPA/ANDY RAIN

Tomas Berdych of Czech Republic returns the ball to Switzerland’s Roger Federer during their match at the ATP World Tour Finals in London, Britain, 15 November 2015. EPA/WILL OLIVER

Switzerland’s Stanislas Wawrinka returns the ball to Spain’s Rafael Nadal during their singles Ilie Nastase group match of the ATP World Tour Finals tennis tournament at the O2 Arena in London, Britain, 16 November 2015. EPA/ANDY RAIN

Britain’s Andy Murray in action against Spain’s David Ferrer during their singles Ilie Nastase group match at the ATP Tour tennis finals tournament at the O2 Arena in London, Britain, 16 November 2015. EPA/ANDY RAIN

Spain’s David Ferrer returns the ball to Britain’s Andy Murray during their singles Ilie Nastase group match at the ATP Tour tennis finals tournament at the O2 Arena in London, Britain, 16 November 2015. EPA/ANDY RAIN