As reported by The Athletic, Downman, who is just 15 years old, suffered the injury following a challenge by an opponent during a friendly against Manchester United on Saturday.
Arsenal's 28 injuries is the highest in the Premier League this season and already includes huge names such as William Saliba, Gabriel Magalhaes and Cristhian Mosquera, as well as Kai Havertz, Gabriel Jesus and now Dowman as manager Mikel Arteta tries to handle so many knocks.
David Ornstein revealed the extent of the injury on Wednesday morning in which is a crushing blow for the Gunners.
"Max Dowman expected to be out for approximately two months after suffering ankle ligament damage. Fifteen-year-old England youth international attacker injured in challenge by opponent in Arsenal friendly v Manchester United - but anticipated surgery not required."
The teenager has been withdrawn from Arsenal's Champions League squad, meaning he cannot play in the competition again until the knockout stages. Speaking earlier this week, Arteta revealed that Dowman is still adapting to the game at the highest level.
"It is part of the journey. I mean at some point when you play at this level, when you play in the position that he plays, when you play the manner that he plays, it was going to happen, and it has happened.
"It's not ideal. He picked up weeks, it could have been worse, and we learn from that and now use this time to continue to improve in his education, in everything that is related to professional football, his habits, the way he needs to develop his physicality as well and the understanding of the game."