McTominay joined Napoli in the final days of the summer market and ended the season a Serie A winner and also named Player of the Year in Italy.
Conte told Sky Italia: "I knew McTominay very well , he grew up in the Premier League with Manchester. I saw that when he played he was always impactful but I saw that he was not used in a decisive way and as a key player by his club. He rarely did it, he was almost never a starter.
"We had spoken about him with (sports director Giovanni) Manna. He had told me that it was a situation that could be done if certain situations combined. Sometimes directors also tell you stories to keep you happy (laughs).
"But if you say to me: did you think he would get to 100%? I would have said no, also because we didn't have the Cups. Instead, in the end he arrived and I was very happy. Manna was very good. I repeat, I didn't think he could arrive."