Nigel Clough has bolstered his defensive options with the signing of Crystal Palace defender Paddy McCarthy on an initial one-month loan deal.
The experienced centre half, currently Neil Warnock's vice-captain at Selhurst Park, has previously represented Charlton Athletic and Leicester City, having begun his career with Manchester City.
The Dublin-born operator recently a contract extension with the Eagles, making him a Palace player until the end of the 2015/16 campaign, although Warnock is keen for him to get out and play some first-team football.
Earlier in his career, the defender, who played for Palace against United's U21s at the beginning of September, was capped by the Irish at U17 and U21 level, prior to becoming a B international for his country.
With a busy period in the fixture calendar, McCarthy's initial month with the Blades could include a total of six Sky Bet League One fixtures and he goes straight into Clough's plans for Saturday's local derby at Chesterfield.
He trained with his new team-mates on Friday morning.
Blades boss Clough commented: "Paddy is a good, solid defender, an experienced centre half and we are delighted to get him, thanks to the assistance of Neil Warnock.
"After injury, Paddy has been fit for quite a while and has played in the first team at Palace this season so he will be ready to go from the off."