Kasami has been in the limelight this week after scoring a stunning volley against Crystal Palace on Monday evening, but Jol insists that the Swiss international must remained level-headed if he is to develop at Craven Cottage.
The 57-year-old told the Daily Star: "He's still not the best player in England, but I think in two or three years, he could be a big player.
"Maybe then, Juventus can come here and pay a lot of money for him. That would be good for everyone!
"I told him to count his blessings and to be happy at that age playing Premier League football. He needs to keep his feet on the ground. He's a very level-headed boy."
The 21-year-old has made 16 Premier League appearances for Fulham.