Sunderland have made a £3million bid for Barnsley defender Alfie Mawson.
Manager David Moyes has turned to the 22-year-old after Brighton refused to sell highly-rated centre back Lewis Dunk.
Moyes wants to sign a defender after Lamine Kone refused the club's offer of a new contract and turned up to training complaining of a bad back, ruling himself out of Sunday's derby with Middlesbrough.
Moyes is understood to have told Kone to stay away from the club until the situation is resolved, while Everton have made an £18m offer for the player.