The Blades have secured the signing of teenage defender Harrison McGahey from Blackpool.
McGahey, 18, arrives on a two year deal (with the option of a third) to add competition for places in United's back line.
Nigel Clough commented: "A number of the coaching staff watched Harrison at the end of last season and he has potential, that's what we see in him. He will admit that he is not the finished article but we are delighted that he has chosen to join us to aid his development.
"Harrison is a big strong defender and there are a number of similar characters at Bramall Lane, from whom he can learn his trade."
McGahey joined Blackpool after spells with Blackburn Rovers and Liverpool. He was handed a senior debut at Bloomfield Road at the end of last season, playing four times as the Tangerines avoided relegation from the Championship.
The Blades were unable to agree a fee with Blackpool and the price will be set by tribunal.
He is United's ninth signing of the summer and the second this week following the capture of fellow defender Craig Alcock.