The 19-year-old attacking midfielder was signed from Fulham earlier this summer.
And Williams has immediately noticed Carvalho's high standards in the first weeks of preseason.
"The lads we have brought in, we have already seen with Fabio training today and yesterday, he is of a high, high standard," Williams told the club's website.
"He's brilliant on the ball. He's getting used to the way we want to play and the way we want to press. I think everyone the club has signed is going to have a massive impact for us."
The Portugal U21 international scored 10 goals in 36 league appearances.