Manchester United boss Louis van Gaal has warned his team they will face a tough test when they take on Cambridge United at the Abbey Stadium.
The Red Devils already suffered a shock exit from the League Cup at the start of the campaign, losing 4-0 at MK Dons, and the Dutchman will be desperate to avoid another early cup exit on Friday.
"It's always tough to play against weaker teams because in the players' minds, it is a weaker team," van Gaal said during Thursday's press conference.
"For example, on Wednesday, PSV Eindhoven – who are no.1 in the league in the Netherlands – lost against no.3 of the second division. It shall happen also in the FA Cup. There are always surprises and I hope we are not the surprise.
"When you see Cambridge and when you analyse Cambridge, they play very direct with long balls. They have five or six players who are taller than 1 metre 90 so for us it will be difficult to defend against.
"That is why you have to prepare yourself very good. It is not so easy to beat Cambridge United.
"I think here the FA Cup is very important for the fans, for the people and also for the players. That is the difference. In Germany it is fantastic that you win the cup, but not like here.
"Also, the attendances are much higher here than in Germany or Spain. Of course, when you play Barca-Atletico Madrid, then there is also a full crowd but there are not many matches in Germany and Spain sold out, and that is the difference."
Meanwhile, the Dutchman says striker Robin van Persie and defender Luke Shaw are both fit and available to start the game.
"We have to wait until training but Ashley Young, Chris Smalling and Jonny Evans are out for sure," he told MUTV.
"Robin van Persie is available, Luke Shaw is also available."
