The 21-year-old defender, who spent last season on loan at Sunderland, has already been the subject of bids from the Black Cats this summer, as well as their rivals Newcastle United.
Sanderson was identified as a possible target for the Blades following the departure of Phil Jagielka, while doubts remain over the immediate availability of Kean Bryan and Jack O’Connell.
Bryan has yet to sign the contract United offered him at the end of last season, while O’Connell has suffered a further setback in his bid for full fitness after United confirmed he has gone under the knife for a second time in a bid to correct a knee issue.
Another defensive option for the Blades, Brighton and Hove Albion’s Matt Clarke, yesterday joined United’s Championship promotion rivals West Bromwich Albion on loan for the season.
And Birmingham, who travel to Bramall Lane on August 7, are looking to enter the race for Sanderson.
As The Star revealed today, United’s hierarchy are beginning to lose patience with Bryan over his failure to sign a new deal to keep him at the club. The former Manchester City defender finally got his chance to impress in a Blades shirt last season, with O’Connell injured, and has been training alone this summer in a bid to keep up his fitness levels ahead of the new campaign.