The Black Cats remain without a recognised senior full-back and are also short of options in other areas of the field.
Lee Johnson looked set to seal a deal for Liverpool defender Tony Gallacher this week, only for reports to suggest that Sunderland pulled out of the move at the last minute in order to pursue alternative targets.
But with just one pre-season friendly remaining, Johnson will be hoping his squad grows in numbers quickly.
When quizzed on any potential incomings earlier this week, the head coach said talks were ongoing with a number of players - while specifically addressing the Gallacher rumours.
"I've seen the media reports, we know of him [Gallacher]," he said.
"He's a player on a list of ten or twelve options.
"We always want two for every position, and the plan is always to go in with probably 20 senior players and maybe four of the better younger ones to supplement that.
"It's a long season and we saw how much those injuries affected us.
"We're in the market, and we'll see what happens.
"Sometimes these things can take a week, two weeks, sometimes they drop in a day.
"We're certainly in the mix for a few and depending on what has happened behind the scenes today, we'll see.
"Watch this space."
So who could be next to arrive at the Stadium of Light? We take a look.