Verstappen's promotion to motor sport's top tier has not been without criticism, but Tost is adamant that the youngster will perform well for the Italian outfit.
He was quoted by NBC Sports as saying: "Max Verstappen did, last week, a test in Adria. He finished by doing 396km without any problem.
"People were really impressed with his performance and now it's in the hands of the FIA whether he gets a superlicence to do the Friday P1 session in Suzuka and then we will see.
"We will prepare him step by step and I am convinced that he is the correct driver for us for 2015."
Verstappen will replace Frenchman Jean-Eric Vergne next season when he becomes F1's youngest ever driver.