Wenger admits badly affected the Gunners' pre-season preparations.
"You want to keep your young players," he said. "When we didn't reach an agreement over a new contract [with Nasri] I prepared myself to face it. But maybe it was more a conjunction of Fabregas and Nasri that got more publicity.
"I knew in May that it could happen. Overall, I knew that Aaron Ramsey didn't play much last year and that he would be in contention if he had a chance not to be injured. In pre-season, I felt that Jack Wilshere and Ramsey worked very well together.
"What we did not expect, of course, was to lose Wilshere on top of that. We had to admit then that we were a little bit exposed, quality-wise and number-wise.
"I hope Samir gets a good reception. I don't know if he will play, but personally I want every player who has played for us to be respected when they come back.
"Samir improved tremendously while he was with us. He has developed fantastically well from a non-scoring player to a guy who could make a decision. He was an important player here and I'm sure he will be for City as well."