The 30-year-old only returned to training with City last week after recovering from the foot injury that ended his loan spell at Everton in January, but he did not travel with the 28-man squad as he continues his rehabilitation in Manchester.
Despite the omission, Maresca has insisted Grealish still has an opportunity to prove himself. The Italian, who has taken over from Pep Guardiola, said the winger remains part of the club's plans for now.
"At the moment, he is here. He is a Manchester City player," Maresca said. "It's my duty to try to coach them. Jack is here. I have a good relationship with Jack. He has a big heart and he is a very good guy. Then we will see what happens."
Grealish has not played a competitive match since January after suffering the injury during his time at Everton, where he had begun to rediscover his form before his season was cut short. The setback also ended his hopes of forcing his way into England's World Cup squad.
The former Aston Villa captain is entering the final year of his City contract, which expires in 2027, although sources indicate no decision has yet been made on where he will play next season. Everton are interested in another loan move, while clubs from the Premier League, Major League Soccer and Saudi Arabia have also made tentative enquiries.
His omission from the tour has inevitably fuelled further speculation over his long-term future, although City maintain the decision was based on his fitness rather than any transfer plans.
Kalvin Phillips was also left behind as he edges closer to another loan move, this time to Championship side Sheffield United. The midfielder has struggled to establish himself since joining City from Leeds United in 2022 and appears to have no route back into the first-team picture.
Meanwhile, Maresca has selected a mix of experienced internationals and emerging youngsters for his first pre-season trip as City boss. Tijjani Reijnders, Mateo Kovacic, Rayan Ait-Nouri, Josko Gvardiol, Antoine Semenyo and Abdukodir Khusanov are all included after their World Cup commitments, while Claudio Echeverri returns following loan spells at Bayer Leverkusen and Girona. Savinho has also travelled despite renewed speculation linking him with Tottenham.
Several senior players, including Erling Haaland, Phil Foden, new signing Elliot Anderson, Rayan Cherki and Nico O'Reilly, have been given additional time off following the World Cup.
City begin the Maresca era against Serie A champions Inter Milan on Saturday before facing the K-League All Stars and Atletico Madrid in Seoul, while Grealish remains in Manchester working towards full fitness as uncertainty continues to surround his place at the Etihad Stadium.
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