The Wales centre-back has one year left on his contract at the Liberty Stadium, so Swansea might be tempted to cash in on him now rather than risk losing him for nothing next summer.

Williams has been linked with a move to Queens Park Rangers but Sky sources understand that Sunderland boss Gus Poyet has made the first move for him.

Williams, 30, signed a permanent deal with the club at the end of the 2007-08 season after a successful loan spell from Stockport County.

He has been a virtual ever-present rock at the heart of the Swansea defence since, and he signed a new contract in 2012 which keeps him at the club until next summer.