Slot, who is currently managing Feyenoord in the Dutch Ereidivisie, will soon be announced formally as Jurgen Klopp's successor.
Van Polen believes his former teammate is the ideal man to take the Anfield club to new heights.
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"I like that and he deserves this too," Van Polen told ESPN after PEC Zwolle's 5-0 defeat at Feyenoord on Sunday.
"Arne has really created something beautiful here. He has got Feyenoord playing football again in a way that they have not often seen in De Kuip.
"I think Arne has gotten enough feathers up his ass, but in addition to being a very good trainer, he is also a very good person - and that is often even more important to me.
He is a sincere and very pure person."