Gennaro Gattuso, a member of Italy's 2006 World Cup-winning side, was placed under investigation while four people were arrested on Tuesday in connection with a match-fixing scandal, Italian police reported.

Gattuso, 35, sacked earlier this season as coach of second division Palermo, is suspected of "associating with criminals with intent to commit sporting fraud".

His agent Andrea D'Amico said: "Rino (Gattuso) is stunned. For the moment we cannot comment, he's waiting to understand (what's happening). The lawyers are in touch with the public prosecutor."

The long-running "Calcioscommesse" saga took a further twist with the arrest of the four, all said to have provided the link between players and a clandestine betting ring.

Police declined to say where the arrests had taken place, but the nationwide operation was led by the Cremona prosecutor's office, which initially uncovered the scandal in 2011.

The four were named as Salvatore Spadaro, Francesco Bazzani, Cosimo Rinci and Fabio Quadri, the news agency Ansa reported.

Gattuso is to be questioned over his links to Bazzani.

"For 30 Serie A matches there was contact between 'Civ' (Bazzani's nickname) and players and officials," said the Cremona public prosecutor Roberto Di Martino in a press conference.

Di Martino said one of the main matches under investigation was between Chievo and AC Milan on February 20, 2011, and a study of mobile telephones revealed that Gattuso, then a Milan player, had been in contact with Bazzani.

Spadaro is said to be linked with the "Bolognese" gang which was involved with former player Giuseppe Signori, who was arrested in 2011 in the initial investigation into match-fixing.

Bazzani has also been linked with Signori, as well as Almir Gegic, the alleged ringleader of another match-fixing gang.

Gegic, a former Serbian footballer who holds Turkish and Slovak passports, handed himself in to police last year following a year on the run.

Rinci, chairman of the Riccione football club, and Quadri both have links with Spadaro.

Gattuso, renowned as a tough-tackling midfielder who spent the best years of his career with Milan from 1999 to 2012, is not the only former player caught up in the latest investigation.

His former Milan team-mate Cristian Brocchi, 37, is also under investigation.

"Cristian is calm. Under investigation does not mean guilty, nor convicted," said his agent Davide Lippi, the son of Italy's 2006 World Cup winning coach Marcello Lippi.

"We are ready to defend his reputation while waiting for prosecutors to do their job.

"I would invite everyone not to jump to conclusions, right now there's nothing serious, just requests for tickets (to matches) from certain people."

Raffaele Grassi, the director of central operations for the police, explained that this investigation was part of a broader one that had already seen 54 people arrested and 120 people put under investigation.

Di Martino said that despite the numerous investigations, also by other prosecutors' offices, and the number of arrests, illicit betting did not seem to be abating.

"I'm not opinionated and I can't start speculating but it's a fact that despite the arrests and investigations, a large number of these people continue to do what they are doing," he said.

"There certainly hasn't been much of a reaction in Italy given everything is continuing as before."

Di Martino previously described the Calcioscommesse scandal as a "bottomless pit", saying it would run on for years.

It originally involved mostly the second and third divisions but also some top flight matches.

Former Italy striker Signori and then-Atalanta captain Cristiano Doni were the most high-profile names caught up in the affair in 2011 and were subsequently given lengthy bans from football.

However, Juventus coach Antonio Conte was later implicated and also banned for four months as the investigation widened.