The star's lawyers suffered a setback against investors, with a judge seeing "strong evidence" that the fee which took him to Camp Nou was higher than publicly stated.
Brazilian investment fund Teisa has won the right to access documentation on Neymar's 2013 transfer from Santos to Barcelona, after a judge ruled that the group may have been cheated by misleading figures.
The group held five percent of Neymar's economic rights while at Santos, and could be entitled to a greater share of the fee if, as alleged, the transfer's real value was in fact much higher than publicly stated.