Nigel Adkins expects a 'tough challenge' on Tuesday night, when Steven Pressley brings his Fleetwood Town side to Bramall Lane.
The Cod Army arrive in South Yorkshire on the back of an impressive win at the weekend and Adkins has acknowledged Town's transformation from non-league.
The United boss also knows one of the visitors main danger men very well, having managed him at a previous club.
Looking ahead the Gaffer remarked: "They have a new manager in Steven Pressley and they had a terrific result at the weekend (beating Burton Albion 4-0).
"Fleetwood have had a meteoric rise through the leagues and have been well backed throughout, so it will be another tough challenge on Tuesday night.
"When a new manager comes in often the performance levels of individuals are raised and collectively as team they tend to get a few positive results.
"Fleetwood are a good side, they get the ball down and play in the middle of the park and in Bobby Grant, someone we know well from our days at Scunthorpe having signed him from Accrington Stanley, they have a player in top form."
But Adkins is demanding a strong opening to the game from his players, as the Blades seek a fourth consecutive home victory in all competitions.
He added: "We are under no illusions about what we will be facing, but we are at home, we need to be positive and start the game well, because as we know from experience already this season, the first goal is crucial."