Kakuta was at Vitesse Arnhem in Holland this season, but the spell was called to a halt early.
Hillion said: "Frankly, I don't know why he put an end to his stay with the Dutch club.
"It is a huge waste. I already said it and I repeat it, he is the most gifted player of his generation.
"He could have been exceptional.
"But talent is not enough. When you pile on failures and there is trouble in any club where you played, you have to ask the right questions and question yourself.
"You can't manage what is on his mind, his entourage or his family."
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