Papachristou, 23, was preparing to head to London for her first Olympic Games when she posted a joke to her Twitter feed. It was about the West Nile virus, and appeared to mock Greece's African immigrant population.
"With so many Africans in Greece, at least the mosquitoes of West Nile will eat homemade food!!!" she tweeted Sunday.
Papachristou has often taken to Twitter to express her support for the extreme right-wing party Golden Dawn, which has recently surged in popularity among Greeks.
In response to criticism by Twitter users who said her joke was racially insensitive, she initially took a defiant tone.
"I'm not a stuck CD! And if I make mistakes, I do not hit replay! I continue playing!" she tweeted on Monday.
By Wednesday, though, she had turned remorseful, saying in a statement on Twitter and Facebook, "I would like to express my heartfelt apologies for the unfortunate and tasteless joke I published on my personal Twitter account. I am very sorry and ashamed for the negative responses I triggered, since I never wanted to offend anyone, or to encroach human rights."
"I would like to apologize to all my friends and fellow athletes, who I may have insulted or shamed, the National Team, as well as the people and companies who support my athletic career," she said. "Finally, I would like to apologize to my coach and my family."
That apology was not enough to save her spot on the Greek Olympic team. The Hellenic Delegations' Administration Board decided to remove her from the team, citing "comments that go against the values and ideals of Olympism."
In Greece, reactions to the tweet and Papachristou's expulsion appeared to split along partisan lines. A spike in illegal immigration from Africa and Asia has contributed to increasing anti-immigrant sentiment among many Greeks.