Arsene Wenger admits he is concerned about "impulsive" Granit Xhaka's temperament ahead of Sunday's north London derby with Tottenham.
Xhaka was sent off last month in the 3-2 win over Swansea and the Switzerland midfielder has regularly shown his feisty side since arriving in the Premier League
Wenger warned Xhaka that he has to keep his emotions in check in what will be his first meeting with Arsenal's closest rivals.
"I'm a bit concerned yes because the discipline is important," he said. "We want to be effective in all positions we face. In derbies it is important to maintain discipline.
"He's quite normally a composed and calm guy - sometimes he has a reaction that is a bit impulsive. He has to work on that and keep control of his reactions in the game."
Wenger also confirmed that Theo Walcott, Santi Cazorla and Nacho Monreal remain injury doubts for Sunday having missed the club's previous two games.
"Walcott the closest, he will have a definitive test today," he said. "Nacho has tests today and tomorrow, then we will decide.
"Cazorla has not practised yet. We will try to go out today and go from there. He is a doubt."
But Wenger is confident that - with or without the trio - his squad has the strength in depth to beat Spurs and maintain their fine start to the season.
"I believe we have an advantage if we are all at our best. I have a squad of 25 players who are all top class," he said.
"A game of this stature is not about 11 players, it is about 25. Olivier Giroud came on against Sunderland and made the difference. Everyone's contribution will be vital."