Arsenal defender Mathieu Debuchy will be out for around three months following surgery on an ankle injury, manager Arsene Wenger has confirmed.
Debuchy, signed from Newcastle for £12million in the summer, was taken off after catching his studs in the turf against Manchester City on September 13.
It had been hoped the full extent of the injury would not prove severe, but the France full-back now faces an extended spell on the sidelines.
Speaking to Arsenal Media, Wenger said: "He had surgery on Friday and will be out for three months. 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 (Calum) Chambers for that."
Chambers is, along with Hector Bellerin, expected to feature for Tuesday night's Capital One Cup tie against Southampton at the Emirates Stadium.
Wenger intends to utilise his squad for the clash against the Saints, who are second in the Barclays Premier League following their win at Swansea.
"Tomorrow night you might see Hector Bellerin, Francis Coquelin and Isaac Hayden. In the squad, we also have Chuba Akpom and Semi Ajayi as well. These are the players that are the closest," said Wenger.
The Arsenal manager also confirmed Nacho Monreal and Yaya Sanogo were still not match-fit, while England forward Theo Walcott should return after the international break from the knee injury which ruled him out of the World Cup.
Wenger is confident 18-year-old Akpom, who impressed during spells at Brentford and Coventry last season, has the needed attributes to make an impact at the top level.
"I am happy that he has developed as a goal scorer, because when he was a younger kid, his problem was finishing. That has gone now," said Wenger.
"He is a very good finisher and he has now to learn the tactical side of his game. Then he will be ready, because he is a huge talent."
As well as Walcott and Alex Oxlade-Chamberlain, Chambers is another Southampton Academy graduate now in the Arsenal squad.
Wenger has been impressed by the calibre of players produced by the south coast club, who also schooled the raw talents of Real Madrid star Gareth Bale.
"I think if you look at the talents they have sold over the years, they could have been contenders to win the Premier League because they lost Oxlade-Chamberlain, Walcott, Bale plus all the players they lost last season, plus all the players they still have. They have done a fantastic job at Southampton, they deserve a lot of credit," said Wenger.
The Gunners boss has been impressed by the achievements of Ronald Koeman, who took over a difficult job in the summer following the departure of former boss Mauricio Pochettino to Tottenham as well as the sale of several key men.
"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," added Wenger, whose side put recent inconsistencies behind them with an impressive 3-0 win at Aston Villa on Saturday.
"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."