The Aston Villa manager admits that neither he nor assistant boss Roy Keane will attempt to influence the teenager's decision about opting for England or Ireland
The 18-year-old is a Republic of Ireland Under-21 international, but is also eligible for his native country England having been born and raised in Birmingham. Lambert believes that Grealish must make the decision himself, and neither he nor Keane are looking to influence the winger's decision.
"It's not something we talk about. Whatever country Jack decides to play for we can't influence; that's up to him," Lambert told reporters.
"He's only 18 so I don't talk to him about his international career. I'm more interested in Aston Villa so it's up to Jack what he wants to do."
The Aston Villa boss revealed that he is more concerned with Grealish's club form, and admits that the 18-year-old could be in line to start against Leyton Orient in the Capital One Cup.
"Whatever road he wants to go down, we'll back it," the 45-year-old admitted,
"But first and foremost he's got to keep doing what he's doing and try and hang onto my squad in the first team.
"I think he's maturing well. He has done okay. He's got miles to go in the game but at this minute he has done alright.
"There is a chance he'll start [Wednesday] if he is okay, and I dont have a problem throwing him in - if I thought that (it was a gamble to play Grealish) I wouldn't have had him against Stoke."