The lawsuit was filed on August 11 with the Labour Tribunal in Barcelona, and the club is demanding that Neymar repay the portion of the renewal bonus he received upon officially signing a new five-year deal with the club last October.
The Brazilian ace has netted three times from his opening two Ligue 1 games as PSG have enjoyed a goal-laden, flying start.
Barca also stated that should Neymar not be able to pay, PSG will be expected to front the cost.
However, after his world-record €222m transfer to PSG went through, Barcelona spokesman Josep Vives confirmed the club would not be making the payment because Neymar had not fulfilled his contractual duties.
However, the Catalan club allege that Neymar is in breach of contract now that he has left.
The club released a statement saying; "The club demands the player return the already paid sum as he has not completed his contract".
The timing and force of Neymar's comments seemed unusual at the time, but they now make ideal sense in light of Barcelona's lawsuit.
2018 crucial for those born in 21st century: Modi
Together we can bring about a positive change. "The corrupt have no place to hide", he said. "India is celebrating honesty today". However, with the regular interaction through the Mann Ki Baat on radio, a lot of what was said seemed repetitive.
The amount is €8.5m in damages, plus an additional 10% in interest. The club also claims that the Paris Saint-Germain subsidiarily assumes payment of these amounts in case the player cannot take over.
"FC Barcelona have taken these steps in order to defend their own interests after Neymar rescinded his contract with the club just a few months after signing a renewal until 2021".
La Liga accused PSG of violating Uefa's Financial Fair Play (FFP) rules and Barcelona previously said they would report the French side to Uefa for a FFP breach. "But with [the board], no".
"I spent four lovely years there and parted happy".
"I am disappointed with them [Barcelona directors]".
"To see my former teammates unhappy makes me sad also, because I have many friends [there]".