He came to Arsenal with a big reputation, he had 75 international caps for his country, a veteran of World Cup and European Championship campaigns.
Arsenal had conceded eight goals days earlier at Old Trafford, and defensive reinforcements were needed. Thomas Vermaelen was out injured, having missed almost the entire season before, and Laurent Koscielny had yet to convince everybody he had what it took to perform in the Premier League after a mixed opening season.
Almost straight away, Mertesacker's performances were underwhelming, with fans criticising his apparent lack of pace and slow turning circle. Wenger knew about his lack of mobility when he was signed, but his key strength was his reading of the game and his positioning, however with him still adjusting to the pace of the Premier League his game was slightly off.
As the season went on, Vermaelen returned in late Autumn, and Laurent Koscielny really stepped up his game. The Frenchman was arguably the most improved player in the whole of the Premier League.
Mertesacker's season ended abruptly, in the 2-1 win over Sunderland in early February, which saw Thierry Henry score a last gasp winner. Vermaelen and Koscielny ended the season with a solid partnership and that was expected to continue this term, with Mertesacker the odd man out.
It has turned out so far not to be the case, thanks to Laurent Koscielny picking up an injury on international duty. Mertesacker has stepped into the breach and performed excellently.
The Mertesacker-Vermaelen axis has been the cornerstone of the Gunners start to the season, not conceding a single goal in three games, despite Vito Mannone deputising in goal for the injured Wojciech Szczesny in tough away games at Stoke and Liverpool. The defensive coaching of Steve Bould has quite rightly been credited with the excellent start.
Koscielny has now returned from injury, and came on in the final minute at Anfield for Vermaelen.
The Belgian, as club captain, is now more or less undroppable, so Mertesacker is the man who finds his place under threat. However with the German performing excellently, and the side yet to concede, it is surely fair comment that Koscielny may not find it easy to dislodge him, regardless of his talent.
What do you think? Should Mertesacker step aside next game, or should Koscielny bide his time and sit on the bench?
image: © Ronnie Macdonald