AZ Alkmaar are demanding £5.9million from Middlesbrough striker Afonso Alves after claiming he broke an agreement to join the club from Dutch rivals Heerenveen earlier this year.

AZ say Alves had agreed in principle to join them during the transfer window, but the Alkmaar club failed to reach a deal with Heerenveen by December 31 and the player instead decided to join Boro.

The case between AZ and Alves has gone to arbitration and the club's lawyer, Eric Vile, said: "We are claiming this amount of money on the basis of FIFA's rules."

The hearing will continue on May 19.