Koscielny last week refused to travel with the club because he thinks his future with the London-based club remains uncertain.
The 33-year-old, who sees his future at Emirates to be in the air, is reportedly being linked with a return to Ligue 1.
But Emery, whose side defeated Colorado Rapids 3-0 in a pre-season match early on Tuesday, disclosed after the game that, the experienced defender is still needed at the club.
"He has one year left on his contract. For me as a coach, he's an important player. Now, it's one matter for him and the club.
“The club and him need to speak, they are speaking about his situation. I cannot say more than that.
“I spoke with him before he came here and he decided to stay there."
With side finishing fifth in the Premier League last season, Arsenal are expected to beef up their squad this summer as they have been linked with Crystal Palace’s Wilfred Zaha.
But the Spanish trainer refused to share light on their recruitment process when asked about the transfer plans of the club this summer.
“The club is working. We are speaking every day with the club and [technical director] Edu. I prefer to work with patience and calm and take the best decision.
“We have very good players, very young good players. We need someone to help us. The club is working on that.
"We prefer to take the best decision with patience. If we need to wait more time for this reason I prefer to do that.”
