United have signed experienced Championship striker Clayton Donaldson.
The 33-year-old has signed a deal until the end of the season with the option for a further year. An undisclosed fee has been agreed with Birmingham City.
Boss Chris Wilder commented: "We have watched Clayton a lot, most recently for Birmingham at Burton, and it is clear that he will be a useful addition for us. He offers additional pace and power at the top end of the pitch and his Championship experience will be of value."
Yorkshireman Donaldson began his professional career at Hull City and spent time out on-loan at Harrogate Town, Scarborough and Halifax Town, prior to making his name at York City, where he averaged just short of a goal in every two games.
A season in Scotland with Hibernian followed, prior to another prolific spell back in England with Crewe Alexandra.
In July 2011 the Jamaican international joined Brentford on a free transfer and during three seasons at Griffin Park he averaged better than a goal in every three games.
The 33-year-old turned down the chance to remain with the Bees in the summer of 2014, opting to join Birmingham City, where he has scored 33 times in 102 league starts in the Championship.
The deal was signed on Thursday night, United's second of transfer deadline day, and tenth of the summer window.