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.
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1. 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
2. Eric Lichaj
Sunderland were linked with the former Aston Villa and Nottingham Forest defender in the summer but a move didn't materialise. Lichaj, 33, last played for Turkish Super Lig club Fatih Karagumruk but left earlier this year. Photo: Dan Istitene
3. Brandon Mason
It's unclear what state the 24-year-old is in after recovering from a hamstring tear in August. After being released by Coventry in the summer, Mason was training with Portsmouth before suffering the setback. He has been posting training videos on his social media account as he eyes a return to action. Photo: Morgan Harlow
4. Emilio Nsue
After playing a key part in Middlesbrough's promotion from the Championship in 2016, the Equatorial Guinea international also had a spell at Birmingham. Nsue, 32, has been playing in Cyprus for the last few years but was released by APOEL Nicosia in the summer. Photo: Nigel Roddis