Sunderland have said that they are "extremely disappointed" following confirmation that Jack Colback has joined Newcastle United.
The midfielder was out of contract at the Stadium of Light, where he has been part of the senior side since 2008.
A statement on the club's website said: "Jack is a player we have nurtured and developed through our academy system since he was eight years old. We gave him the opportunity to become a professional footballer and are therefore extremely disappointed in the events that have led to his departure from the club.
"This wasn't about money, the club agreed to all of the terms demanded of us during discussions and we were always led to believe that Jack wanted to stay with us. At his and his representatives' request, final talks were put on hold until the club secured its top-flight status. To our dismay however, we were subsequently never given the chance to negotiate with him to stay.
"For him to then leave the club that has supported him throughout his formative years in such a manner, with no chance for Sunderland to recover any of the significant investment that it has made in him as a player, has left a bitter taste."
Sunderland secured their top-flight status with a game to spare last season, finishing 14th in the table.
