Arsene Wenger has revealed Laurent Koscielny will be out of action until December after the Arsenal defender had surgery on a ruptured achilles.
The France international had to be taken off the pitch on a stretcher after losing his footing while moving off the ball during the Gunners' Europa League exit against Atletico Madrid last week.
His national team had already confirmed that he will not be available for the World Cup.
Koscielny, who has been nursing an achilles problem all season, has had surgery and will now not be available for Wenger's replacement as manager until the end of 2018.
Speaking on Tuesday, Wenger said: 'Koscielny is devastated because he has surgery and that means he will be out for six months.
'You will not see him before certainly end of December now, beginning of December at best, in certainly his final year when he would play for the national team. He misses now the World Cup as well.
'We always try to be positive, you know, but overall you can only say and try to support people when they suffer because they suffer of course from a situation like that.
'What is unusual in his case is that he had a tendinopathy for a long time and usually they don't go to rupture but in this case... that is a bit surprising in this case.
'When people always have enflamed tendons they don't rupture but in his case I don't know why.'
Koscielny had already said he would retire from his duties for France following the World Cup.
Wenger takes part in his second to last game as Arsenal manager on Wednesday night when his side visit Leicester.