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.
So who could be next to arrive at the Stadium of Light? We take a look.
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. SUNDERLAND, ENGLAND - MAY 09: A General view of the Stadium of Light prior to the Sky Bet League One match between Sunderland and Northampton Town at Stadium of Light on May 09, 2021 in Sunderland, England. (Photo by Pete Norton/Getty Images)
Sunderland hopes of £2million deal fade as defender bid details revealed - plus Sheffield Wednesday, Portsmouth updates Photo: Pete Norton
. Portsmouth target busy end to the window
Pompey chief executive Andrew Cullen says the club are targeting at least five new signings before the end of the transfer window (Portsmouth News) Photo: Bryn Lennon
. Championship club could swoop for ex-Sheffield Wednesday man
West Brom could make their move for Adam Reach - who is a free agent after leaving Sheffield Wednesday (Express & Star) Photo: Alex Pantling
. Wigan Athletic detail ambitious transfer plans
Wigan boss Leam Richardson is targeting 'six or seven' more new signings - having already brought in eight players this summer (Wigan Today) Photo: Lewis Storey
1. Portsmouth target busy end to the window
Pompey chief executive Andrew Cullen says the club are targeting at least five new signings before the end of the transfer window (Portsmouth News) Photo: Bryn Lennon
2. Championship club could swoop for ex-Sheffield Wednesday man
West Brom could make their move for Adam Reach - who is a free agent after leaving Sheffield Wednesday (Express & Star) Photo: Alex Pantling
3. Wigan Athletic detail ambitious transfer plans
Wigan boss Leam Richardson is targeting 'six or seven' more new signings - having already brought in eight players this summer (Wigan Today) Photo: Lewis Storey
4. MK Dons sign striker - with knock-on for Will Grigg
MK Dons have signed Tottenham striker Troy Parrott on loan - in a move that may spell the end of their interest in Will Grigg (Various) Photo: Stu Forster