Neymar has been ordered by a judge to pay Barcelona €6.7 million (A$11m) over a contract dispute with the La Liga champions.
The Paris Saint-German and Brazil forward had claimed he was owed €43.6 million (A$71m) by Barca in unpaid bonuses.
Neymar insisted he was due the huge sum as a loyalty bonus, having signed a new five-year contract with the Catalan giants in 2016.
The Brazil international, who joined PSG for a world record fee of €222m in August 2017, has instead been told he must fork out to his former employers - although an appeal could be lodged.
Barca welcomed the verdict on Friday, stating: "FC Barcelona expresses its satisfaction with the verdict announced today by Social Court 15 in Barcelona in relation to the lawsuit involving FC Barcelona and the player Neymar Jr regarding the amount of the signing bonus in the final renewal of the player's contract.
"The ruling has fully dismissed the player's claim for payment of 43.6 million euros, and has accepted a large part of the defence presented by FC Barcelona, as a result of which the player must return €6.7 million to the club.
"Since the player's representative is entitled to appeal this decision, the club shall continue to fervently defend its legitimate interests."
Neymar's representatives have yet to comment.
Despite their long-running legal dispute, Barca tried to sign Neymar last year and the player even stopped training with PSG in order to try and force through the move, prompting angry protests from the French side's supporters.
The move eventually broke down, with PSG's sporting director Leonardo claiming Barca failed to meet their asking price for the forward, who formed a world-beating attacking trio with Lionel Messi and Luis Suarez between 2014 and 2017.