Vermaelen undergoes ankle surgery
The Premier League club said the Belgian was expected to return to first-team training in around a month, likely ruling him out of Champions League Group F matches at Borussia Dortmund next Tuesday and at home to Olympiakos on September 28.
The centre-back is also set to miss league games against Swansea City, Blackburn Rovers and Bolton Wanderers, as well as North London rivals Tottenham Hotspur on October 2.
"Vermaelen has undergone a minor procedure to remove an inflamed plantaris tendon from his left ankle," Arsenal said on their website on Tuesday.
"This is the same treatment that he had on his right ankle in January this year and has nothing to do with his Achilles tendon.
"The action was taken after consultation with specialists who advised this was the best thing to do to prevent it becoming a persistent problem."
Vermaelen missed nearly eight months of last season with an Achilles problem.
The injury is another blow to Arsene Wenger's side, who have endured a miserable start to the season with poor results, several injuries and suspensions and the departures of Cesc Fabregas and Samir Nasri.