The 20-year-old went down clutching his leg following a challenge with Kyle Walker. He initially tried to play on before being withdrawn for summer signing Stephan Lichtsteiner after 35 minutes.
“Ainsley has sustained a small fracture to his left fibula and will be out for six to eight weeks,” Arsenal said on the club's official website.
The news comes as a blow to the youngster who enjoyed a breakthrough campaign last year and has hopes of becoming a first-team regular under Emery this season.
The club also confirmed that Carl Jenkinson has been ruled out for a similar period of time after he “sustained a significant sprain to his right ankle”, which is likely to scupper any loan move away from the club.
Jenkinson was one of three players — along with Joel Campbell and David Ospina, now of Napoli — who had been informed by Emery that they remained surplus to requirements at the end of the Premier League transfer window.
However it is unlikely the club will now be able to find a short-term deal for Jenkinson given the severity of his injury.
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