Jordan Willis is the only senior centre back currently on the Black Cats’ books, with Tom Flanagan weighing-up a contract offer.
So who could Parkinson be targeting to add some depth to the ranks? Here, we take a look at some of the best centre backs who are currently available as free agents – with some attractive options:
5. Tom Clarke
Released by Preston, the 32-year-old can play at centre back or in centre midfield and would be a valuable asset to any League One side. Photo: Lewis Storey
6. Grant Hall
Another player with vast experience, Hall has recently left QPR - although geography could be a potential factor in any prospective move to the North East. Photo: Lewis Storey
7. Sam Hutchinson
Set to leave Sheffield Wednesday this summer, Hutchinson may well have his sights set on a Championship move - but could be a name on the Black Cats' radar. Photo: Nigel Roddis
8. Max Ehmer
While reports have suggested the former Gillingham centre back is on the verge of joining Bristol Rovers, no deal has yet been announced - meaning a host of League One clubs will be monitoring the situation closely. Could Sunderland be one of them? Photo: Pete Norton