Injury forced the withdrawal of Koscielny from last week’s Champions League match in Germany against Bayern Munich with the score at 1-1 soon after the break.
The Bundesliga champions went on to win the match 5-1.
Arsene Wenger’s side have won just once and lost four times against other clubs currently in the Premier League’s top seven, and the defender noted, “We have up and down results. It’s a mental problem.
“We have the technical and physical qualities. We have to make an effort for the whole game.
“Against big teams you need more than talent. It takes more commitment, helping your teammates to defend. You have to find other reserves.
“In certain games we lacked the knack, determination in challenges. We’re in a difficult situation and we have to stick together. We have to hate losing.”