Mertesacker: Dortmund will be tough

Arsenal defender Per Mertesacker fears that Borussia Dortmund will be a huge challenge for the Gunners, who are preparing for this week's Champions League tie in Germany.

Mertesacker knows of Borussia Dortmund very well, having watched them win the Bundesliga last year.

"Dortmund were the best team in Germany last year, they do a good job passing the ball and have great players," said the former Werder Bremen man.

"It will be difficult for us but I know we have very good players and I'm confident we can get a result.

"Dortmund are the toughest opponent in our group, so we will be very happy if we can take something from this match."