Grealish has been left out of City's trip to Hong Kong and Seoul as Maresca's side prepare for the new Premier League season.
The 30-year-old England winger's absence was interpreted as a sign he will not be part of Maresca's plans in the forthcoming campaign.
But Grealish responded by insisting he is still recovering from season-ending surgery on a foot injury in February.
"Just to let you know I'm still recovering from an injury so I'm not training yet," he wrote in the comments of a subsequently deleted Instagram post on Thursday.
"Haven't been 'left out' so stop talking poo poo thanks."
Grealish made a £100 million move from boyhood club Aston Villa in 2021 and has won three Premier League titles with City.
He was part of City's treble-winning side of 2022-23, but gradually fell out of favour with former boss Pep Guardiola amid reports about his off-field behaviour.
Grealish joined Everton on loan last season, but has been stepping up his rehabilitation in recent weeks in a bid to prove his worth to Maresca.
He is in the final season of his City contract and Maresca said: "At the moment, he is here. I have a good relationship with Jack since I left.
"Also, we keep in touch, and the reason why is because he has a big heart and he is a very good guy."