The England midfielder has claimed he faces a three-month lay-off, while manager Arsene Wenger is reckoning on being without the 20-year-old for "at least six weeks".
Oxlade-Chamberlain has become a regular feature in Roy Hodgson's national team, but the blow that forced him to limp out of the Gunners' 3-1 home defeat by Aston Villa on Saturday could now rule him out of the remaining World Cup qualifying group games.
Wenger attempted to quell fears over a long-term absence when he spoke ahead of the Champions League play-off first leg against Fenerbahce, but hours later Oxlade-Chamberlain detailed on his Twitter page that he was facing three months out of the game.
Oxlade-Chamberlain wrote: "Gutted i'm injured so early in the season, But I'm going to be working hard to hopefully be back playing in 3 months. Thanks 4 all ur support."
It was a different take on his situation to Wenger's own appraisal, after the Frenchman said: "He will be out for at least six weeks, he has a posterior cruciate problem, a ligament which is stretched."
Press Association Sport understands Arsenal will carefully manage the player's rehabilitation following expert medical reports and look to bring Oxlade-Chamberlain back to full match fitness at the earliest possible opportunity.
Nevertheless, on top of the club games he will miss, Oxlade-Chamberlain can expect to be absent from the crunch Group H World Cup qualifiers against Moldova and Ukraine next month.
And barring a dramatic recovery, the midfielder is also unlikely to be available in time for the October dates against Montenegro and then Poland as Hodgson's team attempt to reach next summer's finals in Brazil.
Oxlade-Chamberlain has stayed behind in London while Wenger has taken his battle-ready Gunners to Istanbul for the match against Fenerbahce.
Source: PA
Source: PA