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”.