Auxerre president Gerard Bourgoin called for an investigation on Saturday after his player Kamel Chafni claimed he had been racially abused by an assistant referee.
Chafni, a Morocco international, was sent off following an altercation with the official, Johann Perruax, in the 55th minute of Auxerre's 1-0 loss at Brest in the French top flight.
"There was a serious incident and the player has sworn on his honour," Bourgoin told reporters afterwards.
"It appears that the official told him: 'Sod off, Arab.' If that's the case, it's very serious.