Goal reports that Mourinho was initially keen on signing Alderweireld, but was put off by Spurs’ £75m price tag for the 29-year-old.
United were only willing to pay around £55m for the Belgium international.
The Red Devils switched their attention to Maguire, following his impressive display for England at the 2018 World Cup.
However, they have now been told the defender will not be available for a summer transfer.
Leicester have already lost Riyad Mahrez to Manchester City this summer and have so far failed to identify a suitable replacement for Maguire.
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