Arsenal defender Mathieu Debuchy will be out for three months after undergoing ankle surgery.
The French defender suffered ligament damage in the 2-2 draw with Manchester CIty and saw a specialist who confirmed his need for surgery.
Arsenal manager Arsene Wenger confirmed the injury to the £12m right-back today.
"He had surgery on Friday and will be out for three months," said the Gunners boss.
"A reasonable delay is three months. All went well, but it can be a week or two earlier or a week or two later, but it will be around three months. It is a blow of course, how big it will be we will only know afterwards because it will be down to how well we replace him. We bought Chambers for that."
Nacho Monreal is also set to miss the next four matches, leaving Wenger with very few options in defence. Arsenal now have just four fit senior defenders - Kieran Gibbs, Per Mertesacker, Laurent Koscielny and Calum Chambers.
Hector Bellerin played in the 2-0 defeat against Borussia Dortmund, but was poor and was didn't even make the substitutes bench for the 3-0 win against Aston Villa.
Wenger, who has traditionally played his young players in the League Cup, says some of his kids will get a run out against Southampton on Tuesday night.
"You might see Hector Bellerin, Francis Coquelin and Isaac Hayden," he added. "In the squad, we also have Chuba Akpom and Semi Ajayi as well. These are the players that are the closest."
Monreal, Yaya Sanogo, Theo Walcott and Serge Gnabry are all expected to be back in full training after the next international break, but Olivier Giroud will not play again until December.
Wenger also reserved praise for Southampton and their manager Ronald Koeman as they sit second in the Premier League after five matches.
"They are miracle workers at Southampton and you must say everybody expected them to collapse, they lost the spine of their team, they lost their manager and they bounced back in a such a way. I must say when I saw them against Liverpool where they lost the game, I thought straight away that this team is very strong and very good."
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