Roger Federer could meet Britain's Andy Murray in the Olympic tennis final in a repeat of their Wimbledon showdown earlier this month after the pair were drawn on opposite sides of the competition.
Murray is seeded to meet Novak Djokovic in the semi-finals.
Neither of the singles gold medalists from Beijing will be defending their titles in London.
Rafael Nadal was forced to pull out through injury and Russia's Elena Dementieva has retired.
But the draw is the strongest ever, with 18 of the world's top 20 men and 19 of the top 20 women taking part.