Van Gaal demands United improve at Old Trafford

Van Gaal's side looked as though they would be taken to a third-round replay by their third division opponents before Wayne Rooney scored the winning goal with an injury-time penalty.

Before Rooney scored, after impressive substitute Memphis Depay was tripped by Dean Hammond, United were staring at a sixth 0-0 draw in their last 10 home games.

Many of the home supporters showed their frustration at the performance, as well as giving ironic cheers at belated efforts at goal and van Gaal's final substitution of Marouane Fellaini with Andreas Pereira.

"Players for Manchester United have to cope with the pressure of the fans and the media and it's the same for the manager," said Van Gaal.

"It can have an influence but when you are a player for Manchester United you have to cope with that.

"It's not only frustrating for the staff, it's frustrating for the players, the staff and for everybody."

Van Gaal's side has now won back-to-back games after an eight-match winless run and will be hoping this is the start of a run that will bring them first FA Cup success since 2004.

But following another laboured attacking performance, van Gaal knows there is room for improvement.

The Dutchman, who praised the impact of countryman Depay as he added some much-needed pace and penetration to United's attack, said: "The result was alright but the performance was not alright. It has to be much better.

"It's not good but we have won and that's the most important thing in the FA Cup. You have to be in the next round and that's where we are.

"I know it's difficult when you play matches like this when there are a lot of players behind the ball but when you are Manchester United you have to deal with it.

"We didn't play quickly enough. We didn't move the ball quickly enough. When you move the ball slowly your opponent can react easily. That's what we failed today. But it's not easy.

"When there are 10 players behind the ball it's difficult. It's easier to defend than attack. Everybody knows that."

Van Gaal said that midfielder Bastian Schweinsteiger would be assessed following a knee injury ahead of United's Premier League game at Newcastle United on Tuesday.

Sheffield United, 47 places below United on the league ladder, looked as though they had done enough to force a replay as they looked to add Van Gaal's side to the five top-flight teams they had beaten in reaching the last four of the FA and League Cups over the past two years.

Manager Nigel Adkins, who is aiming to lead the Blades back up to the Championship after a five-year absence, said: "The players worked extremely hard against superior opposition. The grit, desire and character gave the supporters something to cheer about.

"The supporters have got right behind the players and there is a togetherness at the football club.

"Our focus now is on Wigan on Tuesday night and Colchester next Saturday which are two big games for us."