Sunderland could be ordered to pay £8million to Inter Milan for flop Ricky Alvarez.
The winger joined the Black Cats on loan in September 2014, scoring one goal in his 11 appearances and helping them to Premier League survival.
But at the end of the loan agreement, Inter claimed that Sunderland were contractually obliged to purchase the Argentinian on a permanent basis on the back of their survival.
According to the Daily Mail , Sunderland refused and the case has now been taken to the Court of Arbitration for Sport (CAS).
It was claimed that problems with Alvarez's knee and the surgery he underwent as a result invalidated the agreement.
Inter won the initial case during a FIFA hearing but Sunderland refused the verdict.
Being forced to pay would be a bitter blow for Sunderland, who would have preferred to use the money on their relegation-threatened squad.
Alvarez, meanwhile, is currently playing for Sampdoria in Serie A.