Serie A club Napoli came under scrutiny on Wednesday after the country's Finance Police raided the club in relation to suspicions of financial foul play, media reports said.
According to the domestic ANSA news agency, police, who took away a number of documents from the club, were acting on a mandate from the public prosecutor in Naples.
The raid was carried out by Italy's Guardia di Finanza, a wing of the armed forces which deals with financial crime and smuggling and comes under the auspices of the Ministry of Economy and Finance.
Reports said the documents seized are in relation to an investigation into the purchase and sale of rights on the performances of team players, the relationship with player agents and any related financial movements.
Police also carried out searches at the offices of the Italian football federation (FIGC) in Rome.
A FIGC spokesman told AFP: "The police requested copies of contracts between agents, the players and the club and we obliged. That is all we can say on the matter."
Reigning Italian Cup champions Napoli have been one of the top teams in Italy's Serie A so far this season and currently sit joint top with champions Juventus.
Along with Juventus, Napoli are the only other team unbeaten team in the league after six games. They are also involved in the Europa League and face PSV in Eindhoven on Thursday.