Forestieri, who is on loan at the Championship club from Udinese, was tipped for big things when he originally broke into the Genoa team at the age of 17, but has failed to live up to expectations at times.
However, the 22-year-old was instrumental in his side's 2-1 win over Leicester City this afternoon, and Zola believes that there is more to come from the youngster.
"He is a young player who has got a lot of potential but he needs to learn to use this potential," said the Italian manager.
"Sometimes he doesn't but we are here to help him and I am sure he will become better and better. I feel there is a lot more to come from him."
The result leaves Watford 15th in the Championship table.