The amount is understood to relate to a loyalty bonus Neymar received after signing a contract extension in October 2016.
"Barcelona decided to take these actions in defence of their interests, after a unilateral termination of contract urged by Neymar Jr a few months after signing the renewal until the end of the year 2021," a statement read.
Neymar joined PSG on a five-year contract on August 4 following a protracted transfer saga.
The Brazil international's move looked set to be held up after La Liga initially refused to accept the funds for the buyout clause.
The deal finally went through and the 25-year-old scored on his league debut in the 3-0 win at Guingamp.
He also scored twice in the 6-2 victory over Toulouse that leaves PSG top of Ligue 1 on goal difference but the fallout from the transfer looks set to rumble on.
In a further twist, Neymar is also considering a formal complaint to FIFA against his former club Barcelona over an unpaid loyalty bonus, Sky sources understand.