Pierre-Emerick Aubameyang was stripped of the captaincy of the club.
The Gabon forward will not be considered for the game against West Ham.
"We expect all our players, particularly our captain, to work to the rules and standards we have all set and agreed on," read the statement.
In March, he was also dropped.
He missed the win over Spurs for a "breach of pre- match protocol".
The Athletic reported that the boss of the club did not reveal how he broke the rules, but he did say that the player returned late from a trip abroad.
Arteta said after the match that they have certain non-negotiables in the team.
I can't tell you what's happening in the dressing room. I will not say what the violation was.
A new three-year contract was signed by the new member of the team.
He has only scored four goals in 14 games this season.
Manchester City are leading the table with 12 points.
