Greek Olympic officials said Papachristou "is no longer expected to arrive in London" after posting a tweet regarding African immigrants in Greece. A message on the Greek Olympic Web site said such actions "go against the values and ideals of Olympism."
The offending message has been removed and Papachristou has issued a series of apologies.
"I would like to express my heartfelt apologies for the unfortunate and tasteless joke I published on my personal Twitter account," Papachristou said in a posting on twitlonger.com. "I am very sorry and ashamed for the negative responses I triggered, since I never wanted to offend anyone, or to encroach human rights."
Papachristou, 23, finished 11th in the triple jump at the recent European Athletics Championships.