The Sun says the Austrian has turned down United as their search for an assistant for Ralf Rangnick goes on.
The Austrian is currently head coach at New York Red Bulls.
He was approached last week by United to join the backroom staff.
Struber, 44, is close friends with Rangnick - who has just taken over at United for the next six months.
They spent time together at Red Bull Salzburg as youth coach and Director of Football respectively.
But Struber has decided to stay with the MLS side.
That is because he does not want to drop down from head coach to assistant.
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