The Black Cats have seen nine senior players depart over the course of the summer but have thus far secured just three new signings.
Alex Pritchard, Corry Evans and Callum Doyle have all joined the club – but head coach Lee Johnson is keen to see his numbers bolstered in the coming weeks.
It’s understood that Sunderland are close to completing a deal for Liverpool full-back Tony Gallacher, although Johnson wouldn’t be drawn on those reports following the 0-0 draw at Tranmere.
He did, however, admit that the club remain ‘in the mix’ for some key targets and told supporters to ‘watch this space’ when it came to incomings.
"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 'closing in' on key signing as Cats handed boost over ex-Arsenal man - plus Sheffield Wednesday, Portsmouth updates Photo: Pete Norton
. Rotherham United see midfielder bid 'rejected'
Rochdale have reportedly knocked-back a six-figure bid from Rotherham United for Oliver Rathbone. The midfielder has previously been linked with Sunderland (Football Insider) Photo: Nathan Stirk
. Doncaster Rovers closing in on ex-Manchester United man
Former Manchester United man Aidan Barlow is set for a medical at Doncaster Rovers today ahead of signing a contract with the club. The youngster has impressed on trial this summer (Doncaster Free Press) Photo: George Wood
. Midfielder on trial with Cheltenham Town
Daniel Crowley has joined newly-promoted Cheltenham Town on trial. The former Arsenal, Hull City and Birmingham man spent time with Doncaster earlier this summer (Various) Photo: Tony Marshall
1. Rotherham United see midfielder bid 'rejected'
Rochdale have reportedly knocked-back a six-figure bid from Rotherham United for Oliver Rathbone. The midfielder has previously been linked with Sunderland (Football Insider) Photo: Nathan Stirk
2. Doncaster Rovers closing in on ex-Manchester United man
Former Manchester United man Aidan Barlow is set for a medical at Doncaster Rovers today ahead of signing a contract with the club. The youngster has impressed on trial this summer (Doncaster Free Press) Photo: George Wood
3. Midfielder on trial with Cheltenham Town
Daniel Crowley has joined newly-promoted Cheltenham Town on trial. The former Arsenal, Hull City and Birmingham man spent time with Doncaster earlier this summer (Various) Photo: Tony Marshall
4. Fulham defender set for League One trial
Fulham full-back Marlon Fossey is set join Rotherham United on trial with a view to a loan move (Rotherham Advertiser) Photo: Marc Atkins