The Germany international suffered the injury during the Gunners’ friendly against Lens last week and was omitted from the squad that travelled to the United States for a pre-season tour.
Speaking at a press conference in the US on Tuesday, Wenger confirmed that Mertesacker would miss the start of the season. However, while Wenger said that the centre back would be out for "a few months" reports emerged late on Tuesday that the injury may be even more serious than initially thought, with a five-month absence not out of the question.
Mertesacker's injury leaves Arsenal short of options in the centre of defence, with Gabriel Paulista struck down by tonsillitis and Laurent Koscielny afforded an extended break after his exploits with France at Euro 2016.
England Under-21 international Rob Holding, who joined the club from Bolton last week, is expected to be handed an opportunity as a result, with Calum Chambers a potential partner in the centre of defence for Friday's match against the MLS All-Stars in San Jose.