Sunderland have so far been unable to convince Stewart to put pen to paper to a new contract and it is claimed talks between the two parties have now reached an impasse.
The Black Cats could as a result look to sell him now and they are not short of interested parties if they do look to cash in.
Middlesbrough are suggested to be showing the strongest interest, a move which would both keep Stewart in the north east and in the Championship.
Glasgow giants Rangers are also credited with interest as they look to back Michael Beale in the transfer market.
Premier League pair Crystal Palace and Brentford are keeping an eye on proceedings, while Blackburn Rovers and Stoke City are also admirers.
Stewart is settled at Sunderland and prepared to stay, but so far he has not been offered a deal he feels he can accept.
Other clubs are prepared to pay the striker significantly more than Sunderland are putting on the table.
