Patrick van Aanholt 'openly stated' that he did not want to play for Sunderland, chief executive Martin Bain has revealed.
The left-back is nearing a switch to Crystal Palace, in a deal that could be worth up to £14 million for Sunderland.
They are understood to be looking at Diego Contento as a replacement on loan.
The Black Cats had been hoping to keep hold of van Aanholt this month, his pace and attacking making him a valuable asset.
But the player's determination to be reunited with Sam Allardyce has forced the issue and Sunderland now look set to grant him his wish, the Dutchman now set for a medical.
Martin Bain has said: "If a player openly states he does not want to play for our club, then it is clear that we have a decision to make. In this instance and in regard to this particular player, we have done what we feel is right for Sunderland, which will always be our priority."