Chelsea, who finished sixth last season to miss out on the Champions League and 12th in 2022-23, are fourth in the table with 13 points from six games.
Maresca replaced Mauricio Pochettino in June and was tasked with returning Chelsea to the Champions League which they last won in 2021.
"I don't think we can compete with City and Arsenal. City have worked with the same manager for (nearly) nine years, Arsenal for five years," Maresca said ahead of Sunday's game against Nottingham Forest.
"If you want to compete, you need that time. It's a huge difference. I am convinced we cannot compete. The target is to improve and to get close slowly. We are not at this moment ready for that.
"You can continue to improve but at the end, the more time you are together, the better it is."
Chelsea made headlines for loaning out Raheem Sterling to Arsenal and striker Romelu Lukaku joined Napoli, with Maresca also omitting former captain Ben Chilwell from matchday squads.
However, the manager said the team's identity was clear after winning five consecutive games in all competitions with different starting lineups.
"For the first two months, there was a lot of noise around the club. Hopefully, we can continue with the way we are now," Maresca said.
"I was not here last year. The only thing I can say is since we started, I like to be focused and in control. The only part I can control is the football side.
"All the noises around the club are something I cannot control, I don't care about it. I'm already thinking about how we can prepare for the game."
Maresca said right back Reece James had not recovered from a thigh injury and Carney Chukwuemeka, who fell ill before their midweek 4-2 win over Gent, will be assessed ahead of the game.
