The Argentine, who was brought in from Watford during the summer transfer window, has played four times for the Owls so far.
And Carvalhal has been impressed by what he has seen from the diminutive playmaker.
He said: “Fernando can do different things and we don’t have another player in that position in the squad.
“He can link the midfield with the attack. He is important to us. We can play with two strikers and Marco [Matias] to link midfield.
“Fernando in our opinion can be important. He is a special player."
Forestieri has scored once for Wednesday during his initial time in the squad so far, and his performances have caught the eye.
The 25-year-old has been happy to run at defenders, while he has also laid on chances aplenty for his teammates, with his excellent passing.
Forestieri has actually been struggling with a hamstring injury for part of his time at Wednesday, but he should be back to full fitness after the international break.
The Owls take on Hull City at the weekend, and they will be looking to make it five wins in a row by being victorious in the contest.