'It's just a technical decision, nothing else to say,' Maresca said.
Mail Sport can reveal Sterling was left surprised by the omission despite having played in all six of Chelsea's pre-season fixtures.
Raheem Sterling was not included in Chelsea's matchday squad against Manchester City
As a result of the shock axing, it may force the 29-year-old to look elsewhere to secure his future.
Serie A giants Juventus have been linked with a potential swoop for Sterling, although an official bid has yet to materialise.
However, there are less than two weeks remaining in the summer window and should Sterling want a move away, the transfer wheels could turn rather quickly.
The winger moved to Stamford Bridge from Manchester City in the summer of 2022 for a cool £47.5million but has struggled for consistency.
However, Sterling has had to contend with playing under six different managers at Chelsea in just over two years.
Since moving to Chelsea, Sterling has scored 19 goals from 81 appearances across all competitions.
His lack of consistency at club level has also led to Sterling being unable to break back into the England squad.
Having been a mainstay for the Three Lions since 2024, Sterling has not featured in an international fixture since the 2022 World Cup in Qatar.