Presenter Takis Tsoukalas, a well-known supporter of Olympiakos, targeted Thanasis Antetokounmpo with the "racist" remark shortly after he had helped his team, Panathinaikos, beat arch-rivals Olympiakos 93-80 in a EuroLeague clash last Friday.
Giannis Antetokounmpo, who plays for NBA club Milwaukee Bucks, lashed out on Twitter: "I have lost sleep in the last few days over the recent racist incident."
The Antetokounmpo brothers are of Nigerian parentage but were both born in Athens and hold Greek nationality.
Giannis added: "If this can happen to Thanasis, who represents the Greek national team and Panathinaikos with pride and with a smile, I cannot imagine what other people of colour face in Greece.
"I am sad and disappointed but we will not let the negative comments change this family and our love for the country we grew up in."
Come home boys, come home. You are no monkeys. Lol, but will they come? Na beans to play for Greece’s National team where they are steadily paid? Issokay o!