The trial, which is set to open at 10:00 am (0800 GMT) at the Provincial Court of Barcelona, is the culmination of a years-long legal saga over his 2013 transfer from the Brazilian club Santos.
Neymar is one of nine defendants on trial on corruption-related charges, among them his parents and their N&N company, which manages his affairs.
All three are facing charges of business corruption.
Investigators began probing the transfer after a 2015 complaint filed by DIS, a Brazilian company that owned 40 percent of the player’s sporting rights when he was at Santos.
Barcelona said the transfer cost 57.1 million euros, but prosecutors believe it was at least 83 million euros.
The club said it paid 40 million euros to N&N and 17.1 million to Santos, of which 6.8 million was given to DIS.
But DIS alleges that Neymar, Barcelona and the Brazilian club colluded to mask the true cost of the deal.
Among the other defendants are two former Barca presidents, Sandro Rosell and Josep Maria Bartomeu, and ex-Santos boss Odilio Rodrigues Filho.
‘Complicity to defraud’
Neymar, now with Paris Saint-Germain, is expected in court on the first day, although that has not been officially confirmed.
He will testify on either October 21 or October 28, but it is not known if he will have to be physically present. The trial is due to end on October 31.
If convicted, he could face two years in jail and a 10-million-euro ($9.7 million) fine.
Real Madrid president Florentino Perez will take the stand on Tuesday by videoconference to explain how a 2011 secret pre-contract deal between Barca and Neymar influenced the market.
“Neymar Junior, with the complicity of his parents and FC Barcelona and its directors at the time, and Santos FC at a later stage, defrauded DIS of its legitimate financial interests,” said DIS lawyer Paulo Nasser on Thursday.
DIS is seeking to recover 35 million euros.
Set for World Cup
Neymar’s lawyers insist their client is innocent, saying the 40 million euros was a “legal signing bonus which is normal in the football transfer market”.
The footballer is having one of his best seasons since he joined PSG following a world record 222-million-euro transfer in 2017.
He scored the only goal in Sunday’s 1-0 victory over bitter rivals Marseille at the Parc des Princes in Paris. Neymar has nine goals and seven assists in 11 matches in Ligue 1.
But his relations with France international superstar Kylian Mbappe appear to be strained, with the 23-year-old reportedly demanding PSG sell the Brazilian.
Neymar is also expected to play a key role for Brazil at the World Cup in Qatar, as the South American giants seek to win the trophy for the first time since 2002, and the sixth in total.
He will lead the Selecao into their Group G opener against Serbia on November 24.
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