The 21-year-old is enjoying his best spell to date since moving to Craven Cottage on a free transfer from Palermo in 2011, scoring twice in his seven appearances so far this season, including a goal-of-the-season contender against Crystal Palace.
Kasami's current run of form is in stark contrast to the rest of his time in west London as he struggled to force his way into Jol's plans and was loaned out to Lucerne last season in order to get some game time.
Kasami's good start to the season has seen him catch the eye of a number of clubs in Italy, with Juventus reportedly said to be monitoring his progress.
With 18 months left on his contract the Cottagers might be tempted to cash in should an offer come there way, although Jol hopes that isn't the case as he believes Kasami can flourish at Fulham.
"He's still not the best player in England, but I think in two or three years he could be a big player," said the Dutchman.
"Then maybe 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."