Zinedine Zidane's World Cup final assault on Marco Materazzi was provoked by a "very serious" comment made by the Italian defender, according to the French playmaker's agent.
Zidane, 34, floored Materazzi with a butt to the chest in the second half of extra-time in Sunday's final and was sent off, missing a penalty shoot-out in which he would have been expected to take one of France's spot-kicks.
The former Real Madrid star's moment of madness in his last match before retiring may have been provoked by Materazzi calling his sister a prostitute, according to a report on Brazilian television channel Globo.
Although neither player has yet revealed the nature of their disagreement, Fantastico, a programme on Globo, employed lip-reading experts who said footage of the incident showed the Italian twice insulted Zidane's sister.
The programme claimed Materazzi made the same comment twice before then using a "coarse word" at the French player.
Italy went on to win the match on penalties and Zidane's agent Alain Migliaccio confirmed to the BBC on Monday that it had been verbal rather than physical abuse from the Italian defender which had triggered his violent reaction.
"He told me Materazzi said something very serious to him but he wouldn't tell me what," Migliaccio said.
"Zinedine didn't want to talk about it but he will talk about it in the next couple of days.
"He is a man who normally lets things wash over him but on Sunday night something exploded inside him.
"He was very disappointed and sad. He didn't want it to end this way."
Zidane has not given his account of the incident but there have also been reports Materazzi had called him a "terrorist" or suggested he did not have the right to play for France - both insults based on French-born Zidane's Algerian heritage.
Football's world governing body FIFA, meanwhile, has denied video evidence played any role in Zidane's dismissal.
Referee Horacio Elizondo missed the clash with Materazzi and only issued a red card after being contacted by the fourth official at the match.
There had been speculation, from France coach Raymond Domenech among others, that the official had intervened after seeing the incident replayed on the numerous television screens close to the side of the pitch.
But FIFA spokesman Andreas Herren denied there had been a de facto use of video evidence in this case.
"The fourth official saw it as it happened on the pitch and directly advised the referee and the referee took action. Full stop," he said.
"It appears the referee was waiting for the situation to clear up a little bit before taking action."