An investigation was launched last month after leaked WhatsApp conversations suggested financial irregularities.
Prosecutors allege that the transfer fee was artificially inflated by over €20 million through the inclusion of several other players in the deal, a practice known as "plusvalenza" or capital gains inflation.
The case stems from the €76.3 million deal that brought the Nigerian international to Naples from Lille.
Date set for Osimhen’s transfer
According to reports, a tribunal in Rome has now set the first hearing of the Napoli president for December 2, 2026.
The decision to proceed to trial was met with "surprise and dismay" by Napoli, who released a statement expressing bewilderment at the indictment.
"SSC Napoli expresses surprise and dismay at the decision by the Rome Preliminary Hearing Judge (GUP) to order the club to stand trial," the club stated.
"All technical reports, of the highest level, have unequivocally demonstrated the correctness of the club’s actions."
The club's legal team echoed this sentiment. Lawyers Gaetano Scalise, Fabio Fulgeri, and Lorenzo Contrada described the ruling as "stunning".
Speaking to Radio DRC, Fulgeri expressed disappointment but remained confident in their case. "We were confident that the evidence brought to the attention of the judge was quite clear and would aid in our defence," he said.
"The evaluation of sports justice was different in Naples. Inter bought a couple of Roma players, but the prosecutors in Milan demanded the filing and concluded there were no irregularities. Napoli didn't have the same luck."