Politicians, newspapers and fans called for Marchisio to be dropped from the World Cup squad after video suggested he sang "Roma ladrona" - Rome the thief - during the national anthem.
Cannavaro, who is leaving Italy for Al-Ahli after the World Cup, was one of the players around him who turned and laughed after the incident, which he claimed was down to tripping up over the words.
"What simply happened was that during the anthem we were getting our timing wrong," Cannavaro told ANSA news agency.
"We were all losing our place, Marchisio in particular, between the sound of the band and the different tempo of the crowd's singing.
"Because of that, and only because of that, we started laughing. The truth is that this is a ridiculous country."