Four officers from the finance police, which is a wing of the armed forces specialising in financial crime, spent over two hours at the club's offices going through documents at the request of the Public Prosecutors Office in Naples.
Police also spent about half an hour at the offices of the Italian Football Federation (FIGC), taking copies of Napoli player contracts and contracts between players and their agents.
"Today, the Guardia di Finanza (finance police) visited the offices of the club to acquire information regarding proceedings, which have their roots in 2007, by the Public Prosecutor at the Court of Naples of which the details are not known," the club said on their website (www.sscnapoli.it).
"We note that the club and its representatives and executives are not being investigated. The club, behaving as it has since its establishment, is standing alongside the judiciary in any work it undertakes to ascertain the truth."
Local media reported that the authorities were acting on information received as part of a "pre-investigative measure" looking into player purchases and sales by the club.
"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," said an FIGC spokesperson.
Napoli are in Eindhoven on Thursday to play PSV in a Europa League Group F match.
- Italian Football Federation