Simon Grayson has warned Lamine Kone and Wahbi Khazri to "do the right things" if they are to earn moves away from Sunderland.
Kone and Khazri have been tipped to follow Jeremain Lens out of the club as new manager Grayson rebuilds his squad for a Championship promotion campaign at the same time as attempting to cut costs.
Lens completed his move to Turkish side Besiktas over the weekend and both Kone, who impressed in Friday night's 1-1 draw with Derby, and Khazri have also been tipped to leave.
Asked about the pair, Grayson said they had shown "fantastic attitude," but added: "If anybody who has wanted to leave the club wasn't doing the work the other lads were doing, then I would come down on them like a ton of bricks and would make sure that they did the stuff because it's part of the discipline you have to have as a manager.
"And they have to be respectful that if they are wanting to leave the club, they have to do the right things because ultimately if the club wanted, we could hold people to their contracts.
"It's not the right thing to do, I suppose, but I have known it happen that players have rotted in the reserves for a couple of years.
"Every player up and down the country has got a value on their head. We have got a value for all our players and if nobody reaches that value, then they will stay with us.''