According to The Athletic, the 31-year-old has been sidelined by fitness concerns and internal disciplinary issues but is now working towards regaining full match fitness after missing club's recent fixtures.
The England international is currently following an individual training programme, with plans to reintegrate him into David Moyes' first-team sessions early next week.
Grealish has made just six appearances during his second loan spell at Everton this season, struggling to rediscover his best form.
Despite his progress, the former Manchester City star will miss the Toffees' upcoming home encounter against Coventry City.
However, he is targeting a competitive return against Brentford at the Gtech Community Stadium on November 23, following the international break.