The Dutchman is set to take charge of Liverpool to replace Jurgen Klopp in the summer.
However, the 45-year-old has no plans to raid the club that he currently manages when he goes to England.
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"Our belief was and is to make the entire team better," he said to Dutch news outlet AD.
"And these boys have all been given time and attention to improve.
"Feyenoord should mainly ensure that as few players leave as possible.
Then many players will be able to do this with their eyes closed for the next six months."