Forward Neymar is to sue former club Barcelona over a 26m euros (£23.97m) unpaid loyalty bonus included in the contract he signed last November.
It comes after Barcelona said they were suing the new Paris St-Germain player for 8.5m euros (£7.83m), as they want him to return the bonus paid when he signed the five-year extension.
Fifa said it had received a claim from the Brazilian against Barcelona.
PSG broke the world transfer record earlier this month by triggering the 222m euros (£200m) buyout clause in Neymar’s contract.
The 25-year-old won two La Liga titles, three Copas del Rey and the 2015 Champions League during his four years with Barcelona.