Samir Nasri insists Arsenal can no longer afford to spend big in the transfer market.
Nasri completed his long awaited move to Manchester City last week before making his debut in the weekend win at Tottenham.
Arsenal boss Arsene Wenger, meanwhile, saw his side crumble in humiliating fashion at Manchester United with an 8-2 loss, but Nasri says that the club have to change.
The France international insisted it was the right time for him to leave, telling l'Equipe: "Yes, it was [the right time to leave], there are sure signs.
"The departure of Cesc to Barcelona is one of them. The defeat against Birmingham in the League Cup final was very harmful for the minds.
"Arsenal remains a big club, but the building of Emirates Stadium changed a lot of things. It has changed the ambitions, so far. But it is not Arsene Wenger, it is the club's politics, the officials.
"Arsenal doesn't have the same funds. They can't make the same coups as before in the transfer market. They are rather forced to sell their best players and bet on young ones."
Nasri was asked about why did not extend his contract at Arsenal last year, but explained: "Why didn't I extend at Arsenal last autumn? They made me an offer and my advisers made another one.
"In this last one there was a clause that Arsenal officials didn't really accept.
"Then, it lasted. When they came back to offer me again in June, I made my decision. In my mind I wanted to leave, above all after the very difficult end to last season and I also already had nice contacts.
"At first Arsene Wenger wanted to keep me. Then, both clubs needed time to agree a transfer fee.
"My agents worked well. With the lawyers they wanted everything to be in order. When the transfer is big, you have to be patient. I am also happy Arsenal could get a nice fee. I prefer to leave that way than being a free agent. I did the same at Marseille. But that €28million fee doesn't put me under any pressure."
The French star maintains he was delighted to join City, despite links also to their city rivals United.
"From the start there was unanimity about my arrival at Manchester City. The coach, the executive director Garry Cook and chairman Khaldoun al-Mubarak, I felt everyone wanted me," he said.
"The players teased me for my first training session. They said: 'You needed time to come. We are waiting for you for one month and a half'. I know most of them, playing against them.
"Training with all those good players every day, I will improve. During sessions, there is a big intensity. At Arsenal it was already good, but here it is an upper level.
"When we finish the session with a match, you really feel like you're in an official competition. There are 22 players of a very high level. In the Premier League, very few clubs can show such wealth."
Nasri is yet to win a major trophy in his career and he is looking to out that right at City, adding: "You play football because you like it, but above all to win trophies.
"I am still dreaming about a national title, a cup or Champions League just like a kid.
"I want to feel satisfaction of a fulfilled season. Individually being named Player of the Year or being in the team of the league, that is reward but it can't replace the emotion of a trophy."