Former Liverpool and Tottenham midfielder Jamie Redknapp has warned Arsenal will struggle to cope without Francis Coquelin.
Speaking to The Mail, Redknapp suggested Coquelin is the one player Arsenal could least afford to lose.
Coquelin was substituted in the loss away to West Bromwich Albion on Saturday just 14 minutes into the game.
French newspaper L'Equipe report manager Arsene Wenger fears a serious knee ligament injury, while Arsenal themselves are yet to comment.
Redknapp said: "Every team seems to have one player they can’t do without. At Arsenal it’s Francis Coquelin.
"As soon as he went off on Saturday, you could tell things would go wrong. It’s the moment Arsenal fans have been afraid of because they don’t have a player who can do the job he does — and now he’s facing months on the sidelines.
"Every year Arsenal seem to suffer with injuries but they just don’t have the strength in depth in that department."
Coquelin was Arsenal's big success story of last season, even though this time 12 months ago he was on loan at Charlton Athletic.
After his month in the Championship he stepped into Arsenal's team with the side suffering with injuries, and went onto become one of the best defensive midfielders in the Premier League, and earn himself a new deal and a FA Cup winners medal in the process.
His emergence even led to Arsene Wenger electing not to sign another player in his position in the summer, but if he misses a substantial period of time, that decision could prove to be very costly.