And with a range of options being considered, the Black Cats may be eyeing the division above for potential recruits.
So which defenders are currently out of favour at their Championship clubs, and could they prove to be realistic targets for Sunderland?
We take a look at some potential options – simply scroll down and click through the pages to see who could be available:
1. Tom McIntyre
The versatile Scottish defender has appeared just three times for Reading this season, and could be available for a loan move before the window closes. Photo: Alex Burstow
2. Curtis Tilt
Currently on the books of Rotherham United, Tilt has been linked with the Black Cats and former club Blackpool having fallen down the pecking order at the New York Stadium. A loan deal has been mooted for the centre back, who has plenty of experience in League One. Photo: Pete Norton
3. Romoney Crichlow-Noble
The left-back spent much of last season on loan with Hartlepool United, but has been in and around the Huddersfield first-team squad over the summer. Could a move to League One be the next step? Photo: FRANK REID 2019
4. Greg Cunningham
Another left-sided defender, Cunningham has featured just three times for Cardiff City this season and may be a player on the radar of a host of clubs. Financially, though, this could prove a tricky deal to do. Photo: Clive Brunskill