Simon Grayson says the attitude of Lamine Kone and Wahbi Khazri has been 'fantastic' since his arrival on Wearside.
The pair are widely expected to leave the club this month, with Kone in particular the subject of fierce transfer speculation over the last twelve months.
The Black Cats are yet to receive a bid for either player, however, and Grayson insists the Black Cats will not be afraid to be patient in their wait for a satisfactory offer.
He said: "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."
Kone's performance on the opening night of the season drew widespread praise, including from former Black Cats centre-back Wes Brown.
His departure would see Grayson return to the transfer market for a replacement, with Inter Milan's Andrea Ranocchia, who spent the second half of last season on loan at Hull City, the latest name to be linked.