The midfielder, who won promotion from League One at Burton Albion last season, delivered his verdict despite the fact Chris Wilder’s side enter tomorrow’s home game against Fleetwood Town searching for a 11th win in 15 games.
“If your aim is to go up, which is obviously the aim we have here, then you can’t afford to go three, four or whatever games without winning,” he said.
“That’s not the type of division this is because the margins are really slim. If you can do that, maintain good results, then it really does put pressure on others and, over a period of time, it normally tells.”
United have not tasted back to back defeats in the league since August after drawing with Gillingham last weekend. Albion suffered that fate only once - losing to Walsall and Fleetwood - en route to automatic promotion eight months ago.
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Duffy said: “There are always areas where you can improve and get better. I don’t remember opponents scoring wonderful goals, where they’ve carved us open and then slipped someone through with a really good pass, too many times this season so we’ve got to stay sharp at all times.”
Fleetwood have bolstered their top six credentials by signing Wes Burns from Bristol City. Midfielder Markus Schwabl has also arrived from German side VfR Aalen.