Mikel Arteta admitted he dropped Matteo Guendouzi for Arsenal's win over Newcastle because of his poor behaviour in Dubai.
Guendouzi clashed with Arteta and members of the Arsenal coaching staff during a training session during the winter break in the Uniter Arab Emirates.
The displeasure continued later in the day at the team hotel with Arteta unhappy with the young Frenchman's attitude and body language in training.
Guendouzi was left out of Arteta's Gunners squad for the 4-0 victory over Newcastle at the Emirates on Sunday, which came days after Arsenal returned from Dubai.
Arteta has since opened up on the reason for dropping Guendouzi, confirming his behaviour was behind the decision.
Arteta said: "I just do my selection in regard to how they train, play and behave. It was about the way we train."
The Gunners take on Olympiacos in the first leg of their Europa League round of 32 tie this Thursday.
It is unclear whether Guendouzi will be in contention for the match in Greece.
Sunday marked the second time this season the 20-year-old midfielder has been left out of Arsenal's matchday squad.
The first came in Arsenal's convincing 5-0 win over Nottingham Forest in the third round of the Carabao Cup, but this was when former boss Unai Emery was still in charge.
