A billboard depicting Serbian tennis player Novak Djokovic is seen on a building in Belgrade on June 24, 2020. - Novak Djokovic has also tested positive for coronavirus on June 23, 2020 along with Grigor Dimitrov, Borna Coric and Viktor Troicki, after taking part in an exhibition tennis tournament in the Balkans featuring world number one Novak Djokovic, raising questions over the sport's planned return in August. (Photo by ANDREJ ISAKOVIC / AFP)