The highly-rated 19-year-old has represented Ireland's Under-21s, but could still opt for England until he is capped by the Republic in a competitive senior international.
Ireland manager Martin O'Neill is expected to pick Birmingham-born Grealish in his squad for the friendly against USA next month, with a view to using him in Euro 2016 qualifying.
BBC Sport claims that O'Neill met with Grealish and his father in September to discuss a call-up, but agreed to postpone it until the winger had penned his new four-year contract at Villa Park.
Grealish, whose grandfather comes from Gort in County Wicklow, tweeted "COYBIG" (Come on You Boys in Green) following Ireland's last-ditch 1-1 draw in Germany on Tuesday.
The former Notts County loanee has made four substitute appearances for Villa in the Premier League this term.