Paris - Ireland international Simon Zebo was the target of "racist insults" during Racing 92's European Cup match against Ulster in Belfast, the French club confirmed on Monday.
After the match, which Racing lost, Zebo, tweeted: "I hope my ears deceived me with some comments directed my way from the crowd."
He added, in a reference to a Quentin Trantino film, 'Django Unchained': "Django wins in the end."
His Parisian club emphasised on Monday that the abuse came from only a few fans.
"Racing 92, does not want to stigmatise the public at Ulster Rugby as a whole," said the statement. "Simon Zebo's abuse came from only one or two isolated individuals and have been condemned by many Northern Irish fans who have shown their support for Simon."
Zebo is from Cork in the Republic of Ireland. He played eight seasons for Munster and has 35 Ireland caps. His father came to Ireland from Martinique.