Barcelona are suing former player Neymar for 8.5m euros (£7.8m) over his world record move to Paris St-Germain.
The Brazil international made the 222m euro (£200m) move to the French club in August after buying out his contract.
Barcelona now want him to return a renewal bonus he was paid when he signed a new five-year deal just nine months before forcing through the move.
“The club demands the player return the already paid sum as he has not completed his contract,” it said.
As well as the 8.5m euro bonus, the club wants “an additional 10% because of delayed payment”.
The statement continued: “The club also requests Paris St-Germain take on responsibility for the payment of these fees if the player cannot do so himself.”
The lawsuit was submitted on 11 August to the Labour Tribunal in Barcelona.
Following the transfer, Barcelona announced the club was withholding a further 26m euro (£23m) loyalty bonus from the player.
Neymar criticised the directors of the club on Sunday after scoring twice on his home debut for PSG in a 6-2 win over Toulouse.
“I spent four beautiful years there and parted happy,” said the 25-year-old. “But with [the board], no.
“For me, they are not the people who should be there, for the direction of Barca. Barca deserve much better.”
Spanish football journalist Eduardo Alvarez speaking to BBC World Service
I am surprised about this news because this Barcelona board has some history in this type of action.
They sued former President Juan Laporta (seeking to hold him personally responsible for alleged losses during his mandate) and they lost that case.
It was terrible in terms of reputation for the club. Laporta was exonerated. Now, to be suing a former player sounds extremely harsh even if you don’t agree with the way he left.
Barcelona mentioned in their statement that they sent this case to the Spanish authorities on 11 August so maybe Neymar’s words on Sunday after his PSG home debut were a reaction this news?