AZ demanded 7.5 million euros (£5.9million) from the 27-year-old, claiming he had already signed a contract with them when he agreed to join Boro from Heerenveen in January.
The arbitration committee of the Dutch football association (KNVB) ruled there had been no breach of contract as the deal with AZ had not been signed by Alves´ agent, Wagner Ribeiro, leaving it incomplete.
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