The user also posted a doctored image showing a decapitated Federer on his knees on a tennis court, with an axe-wielding executioner next to him.

Federer, speaking at a press conference on the first day of the tournament, with black-suited security personnel looking on, said the run-up to the Shanghai Masters had been different from usual. "Obviously maybe it's a little bit of a distraction, there's no doubt about it. But you have to be aware of what's happening around you," he said.

"But that is the case anyway anywhere I go today with my fame and all that stuff."

Federer, a 17-time grand slam champion, who has a first-round bye, said he first became aware of the issue about 10 days ago, before it hit the headlines. But he said had felt safe in China, and praised the authorities.

"So then obviously it came out in the press. That's when things changed. It became much more public, which I'm a bit disappointed about, that it did come out in the press," he said.

"It was something just very small on a website, nothing clear and concrete, people just debating. That it makes that big news is a bit surprising to me."

Federer's wife and twin daughters have not travelled to China but Federer said that decision had nothing to do with the threats, adding: "It was a last-minute decision for me to come here in the first place."

Federer and Novak Djokovic are the top draws, along with Britain's Andy Murray, fresh from his US Open success.

Federer missed the 2011 Shanghai Masters but has an enviable record at the magnolia-shaped Qi Zhong Stadium, winning two of his six season-ending showpiece titles there before the event shifted to London.