According to a report in the Guardian, Alex Oxlade-Chamberlain has had his knee scan after the injury he sustained in England's friendly against Ecuador yesterday, and the prognosis (for Gooners, anyway) is not as bad as we might have feared at first:
Alex Oxlade-Chamberlain’s World Cup participation is in doubt after a scan showed the knee injury he suffered in England’s 2-2 draw against Ecuador will keep him out for between 10 and 21 days.
England have yet to decide whether to replace him - if he was to miss the minimum of 10 days then he would be out for just the Italy game and they might consider persevering with him.
-- The Guardian
From the timeframe there, it seems most likely that the injury is a ligament strain and not a sprain, so that's good news. What is less good news is that Roy Hodgson is considering still hanging onto Ox for the England squad--I'm not a doctor, and I'm far from impartial here, but my medical advice to Mr. Hodgson is PLEASE, ROY, FOR PETE'S SAKE, DRAFT A REPLACEMENT IN AND LET OX GO GET SOME REST.
We will keep you posted as more news comes through.