Grealish continues to be linked with a move to Tottenham - but Villa are in a better financial position after being taken over during the off-season.
The midfielder, a boyhood Villa fan, starred as Bruce's side got off to a winning start in the Championship by beating Hull 3-1.
The manager stated: "He's matured, which is the big thing. This time last year, he damaged a kidney and was out for months. That was the change in Jack.
"He's a wonderful talent and we'll do our best to keep hold of him, but obviously it's going to be difficult. It's going to be a fraught two or three days.
"We understand the human side. He will want to play in the Premier League, Europe, Champions League.
"The owner has made it clear that he wants him to stay. To be fair to Jack, he has got on with it."