The January arrival from Aston Villa scored twice for Roma in Sunday's 2-2 draw with Napoli.
Former Ajax star Roy, who played in Serie A with Foggia, recalled to TMW: "I coached him for the first time when he was 14 or 15, and what immediately struck me about him was his speed.
"And seeing him on the pitch was scary for his age. He had excellent technique, touch, and shooting. He had it in him. Then there was his mentality: the fact that he came from a truly wonderful family played a role in this."
Roy also stated: "He's perfect for Roma and for Italian football, in my opinion. A great team in Italy, it doesn't matter if it's not Juventus or Milan, he has this personality that fits perfectly with the Giallorossi.
"It's truly a great marriage between Malen and Roma. As soon as I heard he could go there, I thought: this deal will work out great. Italy has a culture that suits him perfectly, more so than the English one."