The Blades have made an early move in the January transfer window, with the permanent signing of a midfielder from a League One rival.
Samir Carruthers has joined United on a three-and-a-half year deal, with the Blades paying MK Dons an undisclosed fee for his services.
The 23-year-old has been a regular for the Dons this season, making 28 appearances and scoring one goal, whilst last season he made 43 appearances in the Championship.
Prior to moving to stadium:mk on a full-time basis in August 2014, following a successful loan spell during the 2013/14 season, Carruthers was at Aston Villa, where he made three senior appearances having impressed for the youth team and the reserves.
The London-born player has also won international honours, being capped by the Republic of Ireland at U19 and U21 level.
Blades chief Chris Wilder commented: "We have tracked and monitored Samir for some time and he is a player who can grow with us, we are delighted that the Board have backed us with this level of investment.
"Samir is the right age, has a great pedigree from his time at Villa and MK and he is an exciting player. He is an attacking midfielder who can fit into a number of positions and we are looking forward to introducing him to our great group."