According to RMC Sport (via Sport Witness), the 25-year-old is reluctant to leave the Hornets as he wants to continue to prove his worth at his current club.
With Marco Silva now in charge of Everton the deal could yet still be completed, with the Portuguese manager partly responsible for Doucoure's form at the start of last season, having played him in a more advanced central midfield role whilst in charge at Vicarage Road.
Doucoure impressed greatly during that time, and continued to shine throughout the campaign, scoring seven goals and providing four assists in 37 league appearances.
The Toffees are not the only club interested in signing the midfielder though, with a number of 'top six' clubs allegedly keen. There have been no bids lodged at this stage, leaving Everton as the sole club in active pursuit.
The Toffees are looking to bolster their squad ahead of the new season, but are yet to make a summer acquisition. If they can't sign Doucoure, Everton will surely look elsewhere, with new sporting director Marcel Brands understood to be keen on delivering new talent at Goodison Park.
Watford meanwhile have made five new signings, most notably Ben Foster from West Brom for an undisclosed fee. They have also signed Adam Masina from Bologna and Ken Sema from Ostersunds FK in recent weeks, whilst allowing Brandon Mason and Mauro Zarate to leave the club.
The Hornets will be keen to fend off bids for Doucoure, as they look to build on a steady, yet unspectacular 14th place finish last season.