Castres president Pierre-Yves Revol has blasted Peter Clohessy after the Munster prop claimed Ismaela Lassissi bit him during their Heineken Cup clash on Saturday.
The Irish side lodged a complaint to the European Rugby Cup on Monday about the alleged incident.
Castres hit back by issuing a complaint to the ERC insisting Lassissi had been the victim of abuse from Clohessy during the game.
Revol said: "I have had many discussions with the club's managers and have seen video evidence. He held Lassissi's shirt and his arm happened to come into close contact with Lassissi's face."
The incident occurred during Castres' Pool four last tie as the Irish side were beaten 21-13 at Stade Pierre-Antoine.
"This complaint is absolute nonsense, Lassissi has always showed impeccable behaviour, he has never received any punishment in his career."
The Frenchman faces a suspension from one to three years if Munster's complaint is upheld.
But Revol does not even want to think about that possibility.
"I don't want to talk about that, Clohessy is the culprit, not Lassissi, who has not done anything wrong at all," he added.