Grealish and Villa finally get their Premier League campaign underway this evening when they host Sheffield United (kick-off 6pm).
Current skipper Grealish last week ended months of speculation over his future by signing a new five-year contract with his boyhood club.
Barry, who made 441 appearances during more than a decade with Villa, thinks keeping the 25-year-old will be crucial ahead of what he believes could be another tough season.
Villa stayed up by just a single point last season and Barry said: "I think this season it's going to be just as difficult for them."
"The important news is Jack Grealish staying – that'll settle everyone at the club, and it'll settle him.
"The speculation around him, as I've experienced as a player, it's tough to keep going on and performing when you've got that outside noise. I feel his game will improve again.”
Villa took their spending for the current transfer window past the £75million mark over the weekend with the signing of Bertrand Traore.
The former Chelsea winger has returned to the Premier League after completing a £17m move from Lyon.
“I’m excited to be back (in England),” Traore said.
“I always wanted to come back to the Premier League.
“I had to follow my own way as well and gain some more experience but I think it is the right time to come back.
“I think I’m coming back as a better player, with more experience. And this is the right place for me to come back. It’s good.”
Traore followed Ollie Watkins, Matty Cash and Emiliano Martinez through the door at Villa.
Boss Dean Smith said: “We’re delighted that Bertrand has chosen to come to Villa. He’s a player with immense talent who will really enhance our attacking options.”