By Giuseppe Muro

Per Mertesacker says it is important Arsenal start their Champions League campaign with a positive result against the team he considers to be “their toughest Group F opponents”.

Arsène Wenger’s side face a difficult trip to Borussia Dortmund on Tuesday night with Marseille and Olympiacos completing one of the strongest groups in recent memory.

Mertesacker, who moved to Emirates Stadium from Werder Bremen at the end of August, knows all about the Bundesliga champions and is expecting a stern test.

“It is very important to start very well in the Champions League,” he told Arsenal Player. “I think Dortmund are our toughest opponents, they were the best team in Germany last year.

“The last two years, they have formed a great team of many young players and they want to increase the performance of their young players.

“They have a great stadium with great supporters and there is always a great atmosphere.”

Arsène Wenger singled out the threat of Dortmund playmaker Mario Gotze on Monday and Mertesacker knows the Arsenal defence will have to keep an eye on his fellow German international.

The 19-year-old has attracted the attention of Europe’s biggest clubs with some impressive performances since breaking into the first team at the age of 17.

“He is a talent,” he said. “I think we will have to defend well to stop him.

“He is very important to them and is a great player for the future. He is very quick, very technical and scores goals.”

The full interview with Per is now available on Arsenal Player. He discusses: the atmosphere Arsenal can expect in Germany, Dortmund's success in the Bundesliga last season, the number of young players in their squad, teenage talent Mario Gotze, coach Jurgen Klopp and the importance of starting well in the Champions League.

Copyright 2014 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source 13 Sep 2011