The Black Cats have made an unbeaten start to their League One campaign, winning two and drawing two of their four games so far, to sit in seventh in the table.
Sunderland are hopeful of earning promotion this season and have made several additions to their squad in the window, as they aim to strengthen.
They now want to make sure they put another centre-back at Phil Parkinson’s disposal before the transfer window closes on Friday evening.
However, the club are operating under financial constraints and it remains to be seen who they can land.
Parkinson has already added Bailey Wright, Morgan Feeney and Arbenit Xhemajli to his defensive department in the window, but is keen to strengthen further.
Sunderland have conceded just once in League One so far this season.
They head to take on Swindon Town at the weekend, playing a team that have let in nine goals in five league matches.