Per joined the Club from Werder Bremen in August.
The 6ft 6in centre back has significant experience at both club and international level, enjoying eight seasons in the German top flight - five with Werder Bremen and three with Hannover 96 - making 221 league appearances in total and finding the net on 19 occasions.
The former Werder Bremen captain also played 53 times in Europe for the Green-Whites, including the 2009 Europa League Final.
With a wealth of experience for Germany, Mertesacker has helped his country to the Semi-Finals of the 2006 and 2010 World Cups and to the Final of the 2008 European Championship.
