Stale Solbakken said Copenhagen needed to be "perfect" to have any chance of upsetting Manchester United in the Europa League.
The Danish side face United in the quarter-finals in Cologne on Monday looking to cause a huge shock.
As they prepare for the 2020-21 Superliga season, Copenhagen overcame Istanbul Basaksehir in the last 16, recording a 3-0 second-leg win on Wednesday thanks to a couple of goals from Jonas Wind and another from Rasmus Falk.
But Solbakken said only perfection would be enough for his side against United, who have lost just one of their past 23 games.
"In order to [beat United] we have to play perfect, we need a bit of luck. We maybe need a United that doesn't fire on all cylinders," he told a news conference.
"We need to be perfect defensively. We need to take one or two or three chances we get during a game like this. The chances are not great, but it's an advantage for us this is not over 90 minutes but 180 minutes.
"But we have a good feeling after the season we had a week's break and when the players returned from that we were able to get a couple of players ready to play that were vital to us before.
"We have a good feeling after the 3-0 victory, but you should not put your house on us. We'll give everything."
Asked about the threat that United pose, he was under no illusions of the task at hand.
"We're having to face the best Premier League team after the coronavirus break," he said. "We've seen, among other things, how they beat LASK 5-0 with their B team, so no matter who they put out on the field, we'll naturally have great respect.
"They have a lot of fast players, they play quickly and are good on the counterattack after Bruno Fernandes signed, and they also combine very quickly around the park. So there's a lot to get nervous about, but we have to stick to our plan and see how far it can take us.
"We're preparing exactly as we usually do for a European match, and we are, as always, well prepared for our opponent."
Copenhagen have already faced British opponents in the Europa League this season, having eliminated Celtic 4-2 on aggregate.