"There's been too much alarmism, it was an action over exposed (by the media), that is well within the normal checks that are carried out not only in sports clubs but also commercial enterprises," Grassani told a local Naples radio station on Thursday.
"Napoli, as was explained yesterday, are completely calm.
"There are no complaints, no one at the club is under investigation and the club has faced every contract negotiation fully respecting both sporting and statutory laws."
Officers from the finance police, which is a wing of the armed forces specialising in financial crime, spent over two hours at the offices of the club and half an hour with the Italian Football Federation (FIGC) in Rome on Wednesday, going through documents at the request of the Public Prosecutors Office in Naples.
FIGC head Giancarlo Abete said the visit had been routine with no cause for concern.
"The visit of finance police to the offices of Napoli and the FIGC was only a routine acquisition of documents," Abete said during a meeting to discuss reforms to the Prima and Seconda Divisione, formerly Serie C1 and C2.
"I am not surprised by the uproar that it created, I would be only if I didn't live in the world of football. In any case there is no cause for concern."
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. Napoli are in Eindhoven on Thursday for a Europa League Group F match against PSV.