The Premier League side, placed second on the English top flight table, take on the Championship Royals at Wembley and Coquelin feels it will be a tricky contest.
"You know the FA Cup, you don't know what to expect - any team is ready for it and it is always a tough game at any stage," he told arsenal.com.
"A semi-final at Wembley will be even tougher. We need to be ready and start on the front foot. Hopefully we can do that and win the game."
He added: "I remember a tough game (against Reading for Charlton). We won 1-0, but to be honest I don't think we really deserved it.
"They put a lot of pressure on us, they have (striker Pavel) Pogrebnyak up front who is a big threat, and on the wings they have great players as well.
"We know it will be a tough game, it is a semi-final and the league you play in doesn't matter.
"Whether you are in the Championship or the Premier League, in a game like this the team who puts the most pressure on and creates the most chances will win.
"If everyone is focused, we know we can get a good result."
Since returning from his loan at Charlton, the French midfielder has made 22 appearances for the Gunners.
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