The pair are close thanks to their time together at Ajax.
Muhren told United Review: "There were lots of rumours and we were not surprised because we know he is a very good manager. He proved that with Barcelona, Bayern Munich and in Holland with Ajax and AZ Alkmaar. He is one of the best coaches around.
"I spoke to him just before he signed for United at the Dutch cup final between Ajax and Rotterdam. I was having a word with him and he said Spurs were interested in him. But I told him, 'If you have a chance, you must go to United because it is the biggest and best club in the world'. He hasn’t worked in England, so I know he is looking forward to the challenge."
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