The 15-year-old underwent a trial with the Potters over the summer and, according to ESPN, he has now signed for the club's academy.
"He's started well, so we're just going to see how he progresses and gets on," said a representative of Ngoy's agency. "In Belgium, he plays for the national team so we've got high hopes for him.
"For a 15-year-old he's very talented. If he keeps his feet on the ground and works hard, the sky's the limit for him.
"He's a young lad, so he's got to keep his feet on the ground, and work hard in order to make it. He's done nothing in the game, in reality, because he's got a long career ahead of him."
Ngoy has represented Belgium at Under-16 level.