According to the official club website, Maitland-Niles has "sustained a small fracture to his left fibula and will be out for six to eight weeks".
Ahead of manager Unai Emery's pre-match press confernce, the medial department issued a statement which entailed the recovery timetable of all their injured player.
Arsenal midfielder Ainsley Maitland-Niles will be out for close to two months due to a minor fracture in his left-leg.
Elsewhere, club captain Laurent Koscielny will be out until November with his troublesome Achilles problem, while forgotten full-back Carl Jenkinson won't be seen again until October, and forward Danny Welbeck is back in training.
He started at left-back with Sead Kolasinac's injury which has put the strain on Nacho Monreal and his probable backup, Stephan Lichtsteiner. This week Nacho Monreal is working every day, training every day with us.
Arsenal lost 2-0 against champions City in Emery's first competitive game in charge.
France global Laurent Koscielny, who missed his nation's World Cup-winning campaign with an Achilles tendon tear, is on the mend and is expected to return to training in November.
Welbeck also resumed training and will be in contention for the London derby when Arsenal travel to Stamford Bridge to take on Chelsea.