An internet user under the name "Blue Cat Polytheistic Religion Founder 07" issued the threat before Federer arrived to play at the Shanghai Masters at the weekend.
Federer was surrounded by heavy security during his practice session ahead of his first match in the competition today.
Shanghai Masters organisers said last week ahead of the competition that they were taking the bizarre threat "seriously" while Federer himself labelled it a "distraction" after arriving in the Chinese commercial hub.
"Obviously maybe it's a little bit of a distraction, there's no doubt about it," Federer said Sunday.
"It was something just very small on a website, nothing clear and concrete, people just debating."
But the user, who has eluded arrest so far, took to China's Baidu.com to apologise for his original posting.
"I have not been arrested," the user said on the site.
"I took the initiative to contact the relevant people to apologise."
The original threat read: "On October 6, I plan to assassinate Federer for the purpose of tennis extermination."
The user also posted a doctored image showing a decapitated Federer on his knees on a tennis court, with an axe-wielding executioner standing next to him.
Federer's wife and twin daughters have not travelled to China but he said that decision had nothing to do with the threats.
A Shanghai police spokesman declined to comment on the case.
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