"The club, through its lawyers, will not rest in its pursuit of the truth surrounding this transfer and the role played in it by all those concerned, and for proper recompense for what happened in this unfortunate incident," said the Boro chief.
The Teesside club want an additional £2m in addition to the £5.5m Liverpool paid for Ziege, as that is the figure they believe he was worth at the time.
They also want an additional £4m for the drop in gate receipts and shirt sales since his departure, idgnoring the fact that such a decrease in interest could have been caused by their poor form that season, finishing 14th in the table.