The Blades are likely to explore the loan market, with a number of Premier League defenders potentially available on temporary deals until the end of the season.
Manager Paul Heckingbottom is aware that his club may need to explore the loan market as they look to best manage their finances.
“We have to respect that. Our job is to work within the limitations of the budget," said Heckingbottom ahead of Saturday's contest with Peterborough.
“You push for it and you ask the question, but ultimately the finances are what they are.”
He added: “Every team is chasing the Premier League and I don’t think you can sacrifice the safety of the club to chase that.”
With the Blades keen to bring in a central defender, we have taken a look at five Premier League centre-backs who could bolster the Blades' defensive options for the remainder of the season.
The Liverpool centre-back has been recalled from his loan at Swansea City after making just seven appearances for the Welsh club in the first half of the season.
He has already been linked with a move to Bramall Lane as he is well down the pecking order at Anfield. He featured regularly for Liverpool last season due to a number of injury problems in the heart of defence for Jurgen Klopp's side.
His move to Swansea last year suggests the Reds are open to sending Williams out on loan again. He made 22 appearances for Liverpool last season, including six in the Champions League.
The 24-year-old has proven himself to be capable of producing in the Premier League and is another Liverpool player linked with Sheffield United this month.
Given the number of defensive injuries in Klopp's side last season, Phillips made 20 appearances last campaign and helped the Reds finish third in the table and qualify for the Champions League.
He is the firm fifth-choice centre-back this season and has made just three appearances in all competitions. His displays last season were rewarded with a new four-year deal at Anfield but it looks as if his future might lie away from Merseyside, with a short-term loan an opportunity for him to showcase his talents.
The 29-year-old defender has become a forgotten man at Old Trafford but made his return to the side at the beginning of the month, as the Red Devils suffered a 1-0 home loss to Wolves.
Jones has made over 150 appearances for Man United and despite being well down the pecking order at Old Trafford a loan move could give him the game time he needs, with the defender's contract set to expire in the summer of 2023.
The defensive midfielder, who can also be deployed at centre-back, has made just four senior appearances for Crystal Palace this season. One of which was a two-minute cameo in the FA Cup against Millwall.
The Dutchman made 33 appearances for Palace in the top-flight last term. His quality and versatility would benefit the Blades while a loan deal could benefit all parties as Riedewald can get more game time, United can bring in an experienced Premier League player and Palace can keep the Dutchman on their books if he can find his form at Bramall Lane.
Injuries have restricted Boly's game time at Wolves this season. He is currently out with a calf problem but reports suggest he will be fit again come the start of next month.
Given his injury issues and his place in the pecking order at Molineux, this is another potential deal that would benefit it all parties. A loan at Bramall Lane could help Boly regain fitness while the Blades can bring in a defender who has played 79 times in the Premier League, keeping 25 clean sheets.