The Belgian defender has undergone surgery on an Achilles injury and will not return until October.
Arsenal will be without Thomas Vermaelen for six weeks
Thomas Vermaelen's father expects his son to be out for up to six weeks after revealing that the Arsenal defender underwent surgery on an Achilles injury yesterday.
The Gunners are yet to publicly confirm how long the Belgian will be sidelined for.
Vermaelen's father claims the 25 year old flew to Sweden to have the surgery on his left ankle yesterday.
He told Belgian website Sporza: "The doctor in Stockholm, where Thomas was operated on last time too, recognised the problem now.
"He would not take any chances and immediately operated on Thomas. He expects a five to six weeks of unavailability."
Vermaelen suffered the injury against Udinese two weeks ago and the club had hoped he would not require surgery given his key role within the Gunners defence.
Should he be sidelined for six weeks, he will miss Arsenal's opening two Champions League group stage games and the north London derby at Tottenham Hotspur on October 2.
The former Ajax man missed eight months of last season with a similar Achilles injury on his right foot, although his current injury is not thought to be as serious.
Vermaelen missed the Gunners' 8-2 mauling at Manchester United nine days ago but has otherwise been an ever present at the heart of Arsene Wenger's defence this term.
Per Mertesacker, who signed just before the transfer window shut last week, is now likely to have to step up to fill Vermaelen's place in the team over the next two months.
The German, who arrived at Arsenal from Werder Bremen for £8 million (Dh47.85m), also has competition from Laurent Koscielny, Johan Djourou and Sebastien Squillaci at centre-back.
The London club have conceded 11 goals so far this season and currently sit fourth from bottom of the Premier League table with one point.