Williams sisters shrug off spying fears

The sisters, among the favourites in both singles and doubles, said they had seen nothing untoward while practising here.

"We don't know. We just follow that yellow ball, we don't look around," said Serena in response to question.

"We're out there; we've been practising the last two days together. The only thing I see is the ball or whoever I'm practising with at the time," she added.

"I don't know who's watching or who's not watching."

Spying allegations have rocked previous events in China with Denmark accusing the hosts of filming a team meeting and training session during last year's Women's football World Cup.

The Williams are in search of their second doubles gold after 2000, when Venus also took the singles title.

They are seeded fifth in the doubles competition, which was won by China's Li Ting and Sun Tiantian four years ago.

Serena has amassed eight Grand Slam titles but lost last month's Wimbledon final to her sister. She said she was highly motivated for the Games and rated them more important than the US Open, which starts on August 25.

"I love playing for my country first of all. This is the Olympics and out of all the trophies I have the gold medal is really the favourite," she said.

"This is a life-changing and life-altering experience to be around so many fabulous athletes that are able to take their games and various sports to the ultimate level.

"It doesn't get better than this so it was a no-brainer it is close to the US Open, but this is for me the biggest thing."

Both sisters said they were carrying knee injuries but gave no indication they would pull out.

"I'm doing much better now. I'm blocking that out – mind over matter," Venus said.