However, Kyle Walker was recalled from his loan spell by Tottenham and Craig Morgan has subsequently been ruled out for up to four weeks through injury.
Ahead of the Blades' Championship fixture against Preston on Tuesday night, Blackwell has set up a deal for a top-flight player.
"I am trying to do something today and will hopefully announce on Tuesday morning the arrival of a young centre-back from the Premiership on loan," Blackwell told the club's official website.
"I won't give his name now just in case it falls through and although he has a good reputation he is only a young lad, a development player at his club.
"He might be able to tide us through for a few weeks when Morgan and Seip are fit and we will be much better off than we are at the moment."
Meanwhile, Blackwell is awaiting the results of scans on Mark Bunn and James Harper after the duo picked up injuries in Saturday's 1-1 draw at home to Derby County.