Borussia Dortmund has struggled in the Bundesliga this season, but Robert Lewandowski believes his former club remains dangerous. 

Dortmund travels to Bayern Munich on Saturday.

"This is an important game: Dortmund are always dangerous," Lewandowski told Sport Bild. "They can beat anyone in a one-off game.

"They have so many players injured and they have the whole season to turn things around.

"It has all gone wrong at the start but Dortmund are always difficult to play against.

"They still have great players, so the biggest mistake for us would be to underestimate them."