Nigel Clough believes Leyton Orient will provide the Blades with a much tougher test on Saturday than they did in the Capital One Cup tie last month.
Michael Higdon, who misses out on Saturday through suspension, scored the only goal of what proved to be Russell Slade's last game in charge of the O's at the Matchroom Stadium as United advanced to round four, but Clough thinks Orient will be a difficult proposition at the weekend as they come to South Yorkshire looking to extend their unbeaten away start.
Speaking at his pre-match press conference, the United boss commented: "It was a strange atmosphere when we played down there in the League Cup and we took full advantage to progress to the next round.
"But things appear to have calmed down at Orient now and in my opinion Kevin Nugent is the best person to carry on the excellent work of Russell from last season.
"They had an exceptional start last term and narrowly missed out on promotion at Wembley and although they probably haven't started as well as they would have hoped they haven't lost on the road and won at Aston Villa in the cup, so they will be full of confidence and determined to extend that sequence."
Clough's believes the visitors main threats will come from three attacking players, all of whom have Premiership experience, the Gaffer concluded:
"Darius Henderson is someone our supporters will know very well, whilst the likes of Jay Simpson and Jobi McAnuff of two other good players who have played in the top flight in recent years, so Orient certainly have some good players.
"Dean Cox is another who had a tremendous season last time around, so we know we will have be at our best defensively to keep another clean sheet at home."