Ten Hag worked with Hato at Ajax and discussed the young Dutch defender after Friday night's preseason friendly defeat to Chelsea.
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He joked: "I bet he regrets not having me at Ajax, given that they haven't won any titles in recent years. When I left, he arrived, but he's developed and progressed very well.
"He was one of the best, perhaps the best player in the Eredivisie. He's so young, but already at a very high level."
He added: "You always need a bit of time, but he has an excellent mentality, so he can develop very quickly. He has all the elements, all the qualities in his game to show that he can become a very successful player.
"I am absolutely convinced that he will be successful at Chelsea. I congratulate Chelsea."