Delph, 20, was signed by former boss Martin O'Neill in the summer of 2009 after only one full season in professional football. There is the chance he could be loaned to a Championship club for first team experience.
The former Leeds United player has struggled with injuries throughout his time at Villa Park, starting only eight Premier League games and making a total of 22 appearances in two years.
McLeish said: "I think it's time for Fabian Delph to show the reason why Villa invested a decent sum of money on a very young player.
"The challenge is there for Fabian. He can certainly tackle as well as pass the ball. He's got that quality. He's got a determined attitude and believes in himself.
"We'll get a good idea in pre-season and will assess him then. I have to assess if he is ready for the Premier League.
"But for him, after his injury problems, to get a full season would be a massive boost to his mental toughness.''