The Zidane mystery: what set him off?

Was it something he said?

With France and Italy level in extra time of Sunday's World Cup final, Zinedine Zidane head-butted Marco Materazzi in the chest and was sent off. France went on to lose on penalty kicks.

The day after, still no one knew what the Italian defender might have said to the French captain.

"The Italians did everything they could do to provoke Zidane," France defender William Gallas said.

Seconds before, Materazzi had wrapped his arm around Zidane just as a French attack on goal passed harmlessly by. The two exchanged words as they walked back up the field, well behind the play. Then, without warning, Zidane spun around, lowered his head and rammed Materazzi, knocking him to the ground.

The Paris-based anti-racism advocacy group SOS-Racism issued a statement Monday quoting "several very well informed sources from the world of football" as saying Materazzi called Zidane a "dirty terrorist." It demanded that FIFA investigate and take any appropriate action.

FIFA, which reviews all red cards at the World Cup, would not comment on the specifics.

"This is a disciplinary matter now. I can't give any statements now," FIFA spokesman Markus Siegler said.

Materazzi, meanwhile, was quoted as denying the terrorist comment.

"It is absolutely not true, I didn't call him a terrorist, I don't know anything about that," the Italian news agency ANSA quoted Materazzi as saying when he arrived with his team at an Italian military airfield.

"What happened is what all the world saw live on TV," the Italian player said, referring to the head-butting.

Zidane's agent, Alain Migliaccio, was quoted by the BBC as saying the France captain told him the Italian "said something very serious to him, but he wouldn't tell me what."

Whatever it was, it was enough to infuriate Zidane.

"Zizou is someone who reacts to things," said Aime Jacquet, Zidane's coach at the 1998 World Cup. "Unfortunately he could not control himself. It's terrible to see him leave this way."

Even with the ejection, Zidane still won the Golden Ball as the World Cup's best player, reports AP.