Veteran Mikel Merino was signed to help the club immediately push for silverware.
However, he is injured with a shoulder problem he sustained in his first training session.
On the recovery, Arteta told reporters: “It’s better, it's a slow process because it's a bone and it takes a while to heal. He is progressing well and is already doing some stuff.
“He is working extremely hard and we're using this time to make sure that he understands a lot of things that he has a lot of questions about, and when he’s back he’s ready to go and impact the team.”
On whether he will be back before the October international break, Arteta stated: “We don't know honestly. It's very difficult to understand the healing of the bone. I think at the moment he doesn’t have a lot of symptoms so you can speed it up very quickly because he hasn't lost anything else but we have to wait and see.”