Chris Wilder has revealed that Clayton Donaldson has been on United's 'radar for a while'.
The experienced striker arrived just before the transfer window slammed shut last week and Wilder believes the Blades patience will be rewarded.
He remarked: "I think everyone knew when Harry (Redknapp) went in at Birmingham City, he was going to be wheeling and dealing and there would be a fair few ins there.
"We kept an eye out as we do in terms of players coming surplus to requirements and with Clayton it became clear there was a possibility to get him out of there.
"I know a lot about him, I've tried to sign him three or four times before, he has a good career, starting at Hull, got his hands dirty at York and has played consistently well in the Championship for the last six or seven years."
The Blades boss added: "He has been at Brentford and Birmingham, two clubs who haven't struggled at all. He is a honest player, he works his socks off, he is honest, he stretches teams and he gives us that bit of pace at the top of the pitch.
"Clayton has been on our radar for a while, we've had to bide our time but it's been worth it, we've only paid a nominal fee for him.
"We had no issues, he came up had a medical and agreed personal terms to the end of the season with a view to next and if he performs he will be here for longer that's for sure."