The Blades are rocked by news that Jack O'Connell will miss the rest of the season.
The 26-year-old suffered a knee injury that caused him to miss the team's 1-0 loss to Leeds United in the Premier League.
"Jack O'Connell is possibly out for the season. He will have an operation on Wednesday and we are looking at six months minimum," said the Blades boss.
"He was having discomfort and some issues with his knee and from a long-term point of view it was not good for him to carry on how it was.
"He's an important part so we need to cover that situation. For him to potentially be out for the rest of the season is a blow.
"I've spoken to the owners, as obviously we've known this for two or three days and we need to bring someone in in that position. We are light and can't solely rely on Jack Robinson playing that position all the way through.
"I've highlighted a couple of players and hopefully the board will agree with my assessment that we need to strengthen."