The 31-year-old, who is on loan from Manchester City, has been absent from Everton's last two matches against Newcastle United in the Premier League and Carabao Cup following a reported breach of club discipline.
Grealish's absence came after an unauthorised absence from training, although Everton have remained tight-lipped about the circumstances surrounding the incident.
Following Everton's victory over Newcastle at St James' Park on Monday, Moyes indicated that Grealish still had a future at the club but admitted he was uncertain when the midfielder would return to action.
Speaking on Thursday ahead of Friday's home fixture against Coventry, Moyes confirmed that Grealish would not be available.
"No, Jack is not available," the Everton manager said.
"I wouldn't give you the plan but we will be working with Jack again soon."
The club had previously explained that Grealish remained unavailable for Monday's match because of a lack of fitness, with Moyes declining to provide further details at the time.
Asked whether the upcoming international break could provide an opportunity to resolve the situation, Moyes said Everton would have to wait and see how developments unfolded.
"We just need to wait and see how things go," he added.
Grealish is attempting to revive his career at Everton after struggling to establish himself at Manchester City, despite joining the Premier League champions for a reported £100 million in 2021.
The England international played a significant role in City's historic 2022-23 campaign, helping the club secure the Premier League, FA Cup and Champions League trophies.
However, his opportunities at the Etihad Stadium became increasingly limited, prompting a move to Everton on loan.
Grealish scored twice in 22 appearances during his first spell with the Toffees last season, but his campaign was cut short by injury.
He returned to Everton for a second loan spell this season, hoping to regain his form and regular playing time. However, the midfielder had made just six appearances before his recent disciplinary problems.
With his contract at Manchester City set to expire at the end of the season, Grealish faces an important period in determining the next stage of his career.
