Injuries to Tom Flanagan, Arbenit Xhemajli and Jordan Willis have left the Black Cats with just two senior central defenders on their books.
Dion Sanderson and Bailey Wright are set to line-up against Doncaster Rovers this evening, with some fans suggesting that the club should launch a foray into the free agent market to bolster their ranks.
Such an option could now be feasible following the overturning of the League One salary cap, which means Sunderland are no longer bound by a spending ceiling of £2.5million per season.
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But speaking prior to a meeting of third tier clubs on Thursday, Johnson wasn’t sure whether the removal of the cap would necessarily mean clubs were free to add to their squads.
And even if sides are given the green light to add new signings, Johnson is keen to avoid adding to his squad unless essential.
"I think all those questions will be posed at that point,” said Johnson of Thursday’s meeting.
"Whether or not the salary cap consideration is still this season because clubs have got their squads.
It may be deemed as an advantage for some of the clubs to change their tact and overspend, as it may be perceived. Or, they may say fill your boots guys and do what you want.
"At the moment, I don't really want to add to the squad if we can help it. Unless, of course, Lionel Messi becomes available for a price we can afford."