Aston Villa are due to face Sheffield Wednesday in the first match of the new season.
Di Matteo is confident that Grealish has the capabilities to make a big impact in the Championship this season.
The 20-year-old is expected to play a crucial role in Villa’s starting line-up over the upcoming campaign.
However, Di Matteo admits that the youngster simply cannot make any mistakes - if he is to be a success at Villa Park.
“In Jack I see a young flower that is blossoming,” Di Matteo said. “He is a very joyful young man and we should not forget he is a young man - we all made mistake when we are young and we use that experience to develop.
“I can only judge on what I have seen and he has been tremendous. He has learned. I think he knows he can’t slip up anymore.”
There is a great amount of excitement about Grealish’s future at Villa, but the prospect has already had a turbulent career.
Grealish broke through into Villa’s line-up under Tim Sherwood, but he fell out of favour last term - with off-the-field controversies not helping his cause to get back into the team.
Grealish is predicted to be a major creative force in the Championship, though, and he looks likely to start in Di Matteo’s first match of the season, which comes against Sheffield Wednesday on Sunday.