Marco Silva is said to want a reunion with the midfielder he managed at Watford, and the Guardian reports that the Everton manager has already had a £30 million offer rejected.
And there is little pressure on the Hertfordshire side to sell, having recently received £20m from Hertha Berlin for Dodi Lukebakio.
The Evening Standard also reports that the lateness of Everton's approach is another thing counting against them, with Watford left with little time in which to secure a replacement.
Everton sold another midfielder, Idrissa Gueye, to Paris Saint-Germain earlier this summer, but have already added Fabian Delph and Jean-Philippe Gbamin in the Senegalese's position.
It means Doucoure could have his work cut out if he is to leave Watford for Goodison Park.
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