United's second transfer deadline day capture is Harry Bunn.
The 20-year-old Manchester City striker joins on a 28-day youth loan from Manchester City.
Blades chief David Weir commented: "It is an opportunity to have a look at a good, young player. He is arriving on the back of an injury but this is a chance to assess him and he offers us striking options."
Bunn scored prolifically for City's U18s and U21s teams before embarking on loan spells with Rochdale, Preston North End, Oldham Athletic and Crewe Alexandra.
Earlier on transfer deadline day the Blades captured he signing of Florent Cuvelier from Stoke City. The Belgian signed a three-year deal after an undisclosed fee was agreed.
The arrivals of Cuvelier and Bunn takes the number of captures in David Weir's reign to nine, and includes fellow loanee Conor Coady, as well Lyle Taylor, Jose Baxter, Stephen McGinn, Febian Brandy, Sean McGinty and Jasper Johns.