Paris Saint-Germain and Brazil football star Neymar and eight others went on trial in Barcelona on Monday charged with fraud and corruption over the player's transfer to Barcelona from Santos in 2013.
Neymar, who arrived in the city early Monday, spent about two hours at the Barcelona courthouse before he was excused by the judge from the rest of the day's session.
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He is scheduled to testify on Friday.
Spanish prosecutors are seeking a two-year prison term and a €10 million ($9.8 million) fine for Neymar. They are also seeking a five-year jail term for former Barca president Sandro Rosell and an €8.4m fine for the club.
The case centres on the claim made by Brazilian investment firm DIS, which owned 40% of Neymar's economic rights when he was at Santos, that it lost out on its rightful cut from the player's transfer because the value of the deal was understated.
DIS is seeking a five-year jail term for Neymar, fines worth €149m in total and for the player to be disqualified from playing for the length of any sentence handed down.
Along with Neymar, 30, the defendants include his parents, representatives of the two clubs, former Barca presidents Josep Maria Bartomeu and Rosell, and former Santos president Odilio Rodrigues.
He laughed when Judge Jose Manuel del Amo Sanchez suggested he must be tired after scoring the only goal in PSG's crucial victory against Marseille on Sunday evening.
"Neymar, with the connivance of his parents and the boards of directors of Barcelona and Santos, betrayed the trust of my clients," DIS lawyer Paulo Nasser told a news conference on Thursday.
"The real cost of the transaction [between Santos and Barcelona] was €82m, and only 17 million appeared as the official transfer."
All the defendants have repeatedly denied any wrongdoing.
Baker McKenzie lawyer Maria Masso -- the firm defending Neymar and his family -- said the player has not committed any crime and that the events being judged took place in Brazil, arguing the Spanish courts lack jurisdiction to prosecute the Neymar family.
Neymar, a key member of the Brazil squad heading to the World Cup in Qatar next month, lost an appeal over the case in Spain's High Court in 2017, clearing the way for the trial.
PSG will face Ajaccio on Friday in Ligue 1 before hosting Maccabi Haifa in a Champions League game on Oct. 25.
On Monday afternoon the court is due to hear from Andre Cury, Barca's former point man in Brazil, whose testimony on the transfer negotiations are expected to be central to the case.