Germany's Alexander Zverev and Jan-Lennard Struff with Serbia's Novak Djokovic and Nikola Cacic after their group stage doubles match. Reuters
Germany's Alexander Zverev and Jan-Lennard Struff with Serbia's Novak Djokovic and Nikola Cacic after their group stage doubles match. Reuters

ATP Cup: Novak Djokovic wins but Germany end Serbia's title defence, Rafael Nadal still 'not well enough to play'