The defender has taken some time to settle since his £8million move from Werder Bremen on the final day of the summer transfer window, most recently when he failed to deal with Steve Morison for Norwich's opener in Saturday's Premier League match. Mertesacker brings with him vast experience of the European game, and is in contention to feature against Borussia Dortmund in Wednesday night's Champions League clash, which could see Arsenal qualify for the knockout stages. While Wenger accepts sometimes the 27-year-old has been caught out of position, notably for a couple of the goals in the 5-3 win at Chelsea before the international break, the Arsenal manager maintains Mertesacker brings with him a "commanding influence" at the heart of the defence. "I feel people have been harsh in their judgement," said Wenger. "I like Per very much, because he is a very intelligent boy and reads the game very well, has a calming influence, a commanding influence. "Because he is so tall, sometimes in one situation if he looks a bit not so good, people make a definite negative judgement. "He grows stronger in every game and we watched him again in Germany against Holland, and he had an outstanding performance. I am really happy with him." Belgian international Thomas Vermaelen has just returned to the side after injury, and played alongside Mertesacker in the goalless draw with Marseilles at Emirates Stadium before the international break. Laurent Koscielny and Johan Djourou provide Wenger with plenty of options at the heart of the rearguard. Vermaelen told Arsenal Player: "The boss now has a lot of choices, whereas in the past, he only had a few because of injuries. "Now, everybody is fit, and there is a lot of competition between the centre-halves. "That is only good for the team that there are a lot of options for who is going to play. "You can rest some players at moments when they are a little bit tired. "We all train together and know each other's qualities, so it is not a big problem if you have to rotate." Victory over the Germans on Wednesday night would see Arsenal through to the knockout stages, although not necessarily guaranteed top spot in Group F ahead of the final match at Olympiacos. Despite Dortmund having lost both of their away European ties so far, Wenger is not taking anything for granted. "We have a good opportunity to qualify against Dortmund, but it will be a tough match because Dortmund are a very good side," said Wenger, his team having drawn 1-1 in the BVB Stadion in September. "Also they play as well for their last chance to qualify."
