Dennis Cirkin, Niall Huggins and Denver Hume are all expected to be sidelined until the new year, leaving Black Cats boss Lee Johnson with a big dilemma.
The Sunderland boss deployed Luke O’Nien at left-back during the weekend’s 2-0 win over Ipswich, while Carl Winchester has been moved to right-back this campaign.
Still, Johnson has a concerning lack of options in that area with games starting to come thick and fast ahead of the winter months.
Johnson has admitted he could be forced to change his side’s formation to accommodate his lack of senior full-backs, while Sunderland could also explore the free agent market.
The Black Cats won’t be able to sign players from other clubs until January but could bring in players who aren’t under contract.
Here are nine players they could look at.
A message from the Football Clubs Editor
Our aim is to provide you with the best, most up-to-date and most informative Sunderland AFC coverage 365 days a year.
This depth of coverage costs, so to help us maintain the high-quality reporting that you are used to, please consider taking out a subscription to our new sports-only package here.
Your support is much appreciated. Richard Mennear, Football Clubs Editor


. Andre Wisdom
The Liverpool academy graduate made 38 Championship appearances for Derby last season and was reportedly in talks with the Rams over a new deal. Nothing was forthcoming, though, and the 28-year-old right-back has been a free agent since the summer. Photo: Alex Pantling

5. Martin Cranie
An experienced defender who has played across the backline and as a holding midfield. The 35-year-old made 23 Championship appearances for Luton last season. Photo: Julian Finney

6. Ahmed Elmohamady
A player Sunderland fans will know well following his time on Wearside between 2010 and 2013. Now 34, Elmohamady left Aston Villa at the end of last season after making over 100 appearances for the club. Photo: TIM KEETON

7. Julien Serrano
Released by Monaco at the end of last season, the 23-year-old is still assessing his options. Serrano spent last season on loan at Scottish side Livingston, where he made 24 SPL appearances at left-back and chipped in with four assists. Photo: Getty Images

8. Gaetano Berardi
Following his move to Leeds in 2014, the Swiss defender, who can play at centre-back or left-back, made 157 appearances for The Whites and helped them win promotion to the Premier League. Now 33, Berardi wasn't offered a new deal in the summer. Photo: Stu Forster