Press Association Sport understands the club will reluctantly listen to offers for the 23-year-old after the academy graduate intimated he saw his future elsewhere.
Manager Paolo Di Canio had wanted to extend Colback's contract but with only 12 months now remaining on it the Black Cats would rather sell him now than allow him to leave for free.
Colback has been with Sunderland since the age of 10 but found opportunities in midfield difficult to come by last season and he played a chunk of the campaign as an emergency left-back.
Di Canio had hoped to give Colback more of a run in his preferred position, especially with the likely departure of Lee Cattermole this summer, but the player feels he needs a new challenge.
- Sports & Recreation
- Paolo Di Canio