The Frenchman had been tussling with Diego Costa throughout the opening exchanges of Thursday nights match in Madrid, though hit the turf entirely of his own volition off the ball.
Koscielnys ankle – he has been nursing an Achilles problem for almost two years – appeared to give way, with his entire leg buckling beneath him, and he immediately dropped to the floor in clear discomfort.
Costa beckoned for his teammates to put the ball out of play and waved for the medical team to run onto the pitch.
Koscielny was slamming the pitch in agony and looked utterly distraught, before finally being taken off the pitch on a stretcher after several minutes of treatment.
Arsene Wenger could see that Koscielnys night was over and called on Calum Chambers to replace the skipper.
The scenes were reminiscent of former Gunner Alex Oxlade-Chamberlains injury picked up for Liverpool against Roma in the first leg at Anfield.
That ligament injury has ruled Oxlade-Chamberlain out of the World Cup and there will be serious concerns that not only is Koscielnys season over, but his hopes of going to Russia this summer too.
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