Sir Alex Ferguson has targeted the raiding left back amid fears that Patrice Evra could leave for Real Madrid at the end of the season.
But AC Milan see Coentrao as a successor to the great Paolo Maldini, who has not been adequately replaced since retiring last year.
Looking for guidance: A host of Europe's top clubs are on the hunt for Fabio Coentrao
Chelsea were interested in the summer till they secured Ashley Cole's future and Juventus, Real Madrid and Manchester City have also been linked - promting Milan to consider paying up his release clause in January.
The 22-year-old can leave Benfica for just over £25million, but the Portuguese champions would rather sell unsettled centre half David Luiz - who is most strongly linked with City.
Coentrao came through the ranks as a winger, but has developed as an attacking full back at international level and impressed at the World Cup.
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