The Iran international was signed from Wolfsburg in the summer and after a slow start to life in west London has started to find his feet in recent weeks.
He enjoyed one of his most influential performances in the 2-2 draw at Sunderland at the weekend, winning Dimitar Berbatov's penalty opener before playing a part in Fulham's second, to prompt praise from his boss.
"I feel Dejagah is a marvellous player," Jol told the club's official website. "The only thing is I want more goals, more assists, for him to be a bit more productive, and he's starting to do that.
"Dejagah was always a good player for Wolfsburg. He was always talented, the only thing was that he needs to be a bit more productive. He's got a great shot but he never shoots.
"He's capable of making a lot of assists and we've got him for three or four years so I've got that in his mind that he will improve in England and that is what he wants as well."