Per Mertesacker and Laurent Koscielny have been a rock over the past month or so .
Per Mertesacker and Laurent Koscielny will need to be at the top of their game once again when they face Robert Lewandowski .
Per Mertesacker and Laurent Koscielny have been a rock over the past month or so and will need to be at the top of their game once again when they face Robert Lewandowski .