Bayern extended their lead at the Bundesliga summit in midweek with a 1-0 victory at Borussia Dortmund, opening up a seven-point advantage with six matchdays to play.
The Bavarians could take a major step towards their 30th top flight league title with another win against 16th placed Fortuna Dusseldorf.
Flick was wary of Fortuna, who may be in a battle to avoid relegation, but are unbeaten since the restart, collecting five points along the way. Fortuna are also undefeated across their past six league games.
“From our analysis, I think Dusseldorf make it very difficult for the opponent to build a constructive football game,” Flick said.
“It’s important we act in a focussed manner and work as a team on the pitch, everyone has to get involved.
“The Dusseldorf team are good on the ball if you let them have it. We have to stop that.”
Flick refused to elaborate on any team news with rotation likely after the midweek game, but Thiago has been ruled out with muscular problems.
Fortuna boss Uwe Rosler, who’s appointment in January has coincided with his side’s improvement, said he had a game plan to cause a “surprise” against reigning champions Bayern.
“We are difficult to play against,” Rosler said.
“With willpower we can make it difficult for Bayern as well.
“We will develop a battle plan that will help us create a surprise.”
Elsewhere, second-placed Dortmund are away to bottom club Paderborn on Sunday, while third-placed Leipzig go to Koln on Monday.