Middlesbrough boss Gareth Southgate insists record signing Afonso Alves is their player.
Alkmaar have announced they will take their case to FIFA, despite the Dutch FA having already ruled that the agreement between the player and AZ is invalid because the club failed to meet certain conditions.
Speaking to Dutch newspaper De Telegraaf, chairman Dirk Scheringa said: "He really has a chance of getting banned from playing for the rest of the season. We have a water-tight contract with him."
Alves disputes the claim and his new boss Southgate, when asked about Scheringa's threat, said: "Well, that can't happen. The only thing that can happen is there could be compensation between Heerenveen and Alkmaar.
"The player has got international clearance and is registered to the Premier League so there's no way that can happen."