Roger Federer is back at Wimbledon a few weeks after winning his seventh title there, opening his bid for Olympic gold against Colombian Alejandro Falla.
Serena Williams, who also won at the All England Club, plays Jelena Jankovic in the first round.
The draw was held Thursday, two days ahead of the event.
Federer regained the No. 1 ranking with the Wimbledon victory, elevating his Grand Slam title haul to 17. He won Olympic gold in doubles in 2008 with fellow Swiss player Stanislas Wawrinka. A medal in singles is the one important accolade to elude him.
Falla pushed Federer to five sets before losing in the first round at Wimbledon in 2010.
"He is the favorite whenever he plays," said Falla, who describes this season as his strongest yet. "I know him well and he knows me well too.
"I'm going to have to play my best tennis if I am going to have a chance to win, but he's Roger and he's just won Wimbledon for the seventh time here."
Second-ranked Novak Djokovic of Serbia was drawn into the same half as Wimbledon finalist Andy Murray, meaning the pair could meet in the semifinals.
Djokovic plays Fabio Fognini of Italy in the first round, ahead of a possible second-round match against American Andy Roddick.
Olympic gold medalist Rafael Nadal pulled out because of injury, leaving No. 4-seeded David Ferrer as the highest-ranked Spaniard in the Olympic draw.
Williams could meet No. 1 Victoria Azarenka of Belarus in the semifinals. In the other half of the women's draw, Wimbledon finalist Agnieszka Radwanska of Poland and No. 3 Maria Sharapova, who completed a career Grand Slam by winning the French Open this year, could face each other in the penultimate round.
Serena and Venus Williams are unseeded in the women's doubles. The draw for the mixed doubles will be held Tuesday.
Photograph: Stefan Wermuth