Greek triple jumper Voula Papachristou has been expelled from her country's Olympic team over comments she posted on Twitter which were deemed racist.
Papachristou was due to compete in the London 2012 Games, which officially start this Friday.
But the Hellenic Olympic Committee said her posts mocking African immigrants and expressing support for a far-right party went against the Olympic spirit.
Papachristou has apologised for the "unfortunate and tasteless joke".
As well as the comment on Sunday referring to the West Nile virus and Africans living in Greece, Papachristou had also reposted a tweet by Ilias Kasidiaris, a politician with the far-right Golden Dawn party, criticising Prime Minister Antonis Samaras's stance on immigration.
She had previously retweeted several links to videos promoting the views of Golden Dawn, which won 7% of the vote in Greece's recent elections, and had directly communicated online with Mr Kasidiaris.
Mr Kasidiaris gained notoriety for slapping one left-wing woman politician and throwing water over another, during a heated debate on a television show.
Papachristou tweeted him on his name day last week: "Many happy years, be always strong and true!!!"
The athlete's remarks had prompted calls from the public and within the Greek government for her to be thrown out of the team.
The head of the Greek committee, Isidoros Kouvelos, said the 23-year-old had "showed no respect for the basic Olympian value".
"She made a mistake and in life we pay for our mistakes," he told Skai TV.
Earlier in the week, Papachristou had responded online, saying "that's how I am" and that she was not like a stuck CD: "If I make mistakes, I don't press the replay! I press Play and move on!"
But in a statement on her Facebook page and Twitter on Wednesday, Papachristou said she was "very sorry and ashamed for the negative responses I triggered, since I never wanted to offend anyone, or to encroach human rights".
She apologised to her friends, family, fellow athletes and the national team, but said it would not have been possible for her to compete if she did not support the values of the Games.
"Therefore, I could never believe in discrimination between human beings and races."
The Greek committee said she had been "placed outside the Olympic team for statements contrary to the values and ideas of the Olympic movement".
However, her coach George Pomaski said the punishment had been too harsh and she had already apologised.
"This is a big disappointment not only for her but for her family and for myself, and anyone involved in the Greek team," he said.
Mr Pomaski said he had been unable to contact Papachristou for several hours.
The BBC's Mark Lowen in Athens says Greece is experiencing a sharp rise in racism, with the popularity of right-wing parties such as Golden Dawn soaring.
The government has come under pressure to crack down on racism in all domains, including sport, says our correspondent.