Laurent Koscielny was an unused substitute for France against Serbia on Monday night as he continues to suffer from the back problem that ruled him out of the game against Liverpool.
According to L’Equipe, the centreback was not used due to pain in the psoas [translation via Sport Witness], the muscle that runs around the base of the spine.
It is not clear if the problem, which was not enough to keep him out of the squad altogether, will rule him out for the weekend’s game against Stoke at the Emirates, however it is slightly concerning that it is still causing him pain.
The good news, however, is that most treatments to resolve the issue revolve around trying to get the muscle to relax as well as helping to strengthen and stretch it and we can assume by his inclusion in the French squad that it is not any more serious than that at this point.
As stated on Somatics.com
The psoas muscles have gotten a lot of recognition, these days — often cited as the cause of back pain. If you have both tight psoas muscles and pain around the pelvic rim or in the hip joint, it’s likely you have a twisted sacrum* (S-I joint dysfunction) — a common condition. In that case, tight psoas muscles are an effect of a twisted sacrum, not the underlying cause of the pain, and your psoas muscles can’t be released without first correcting sacrum position. Movement patterns and muscle tensions maintain sacrum position, so mechanical adjustments are of limited effectiveness.