Reports in the Spanish media said that Neymar had filed a lawsuit via FIFA against Barca for an unpaid loyalty bonus of 26 million euros ($30.69 million), which was included in the last contract the player signed with the Catalan side in November 2016.
FIFA confirmed to Reuters that they had "received a claim from Neymar against FC Barcelona" and said the matter was being investigated.
PSG smashed the world transfer record earlier this month by triggering the 222 million euro buyout clause in the contract.
On Tuesday, Barcelona said they were suing Neymar for 8.5 million euros as they want him to return the bonus he was paid when he signed the five-year deal.
The bonus Barca referred to is separate to the 26 million euro payment, according to reports in Spain.
Neymar's management group N & N Consultoria responded in a statement on Tuesday that the player had fulfilled the terms of the contract, as well as stating it was planning legal action.
The player's lawsuit against Barca is the latest chapter of an increasingly bitter split between Neymar and the club which catapulted him to world fame by signing him from Santos in 2013 and with whom he won two La Liga titles, three Copa del Reys and the 2015 UEFA Champions League.
The Brazilian launched a tirade against Barcelona's board and president Josep Maria Bartomeu after starring on his home debut for PSG last Sunday in a 6-2 win over Toulouse.
He said: "I am disappointed with them (Barcelona directors). I spent four very happy years there and left happy, but not with them.
"For me they shouldn't be in charge of Barcelona. Barca deserve much better and everyone knows this."
