However, according to L'Equipe, Monaco are hoping to clinch a deal to sign him this summer so he may leave before ever appearing for the first team.
Watford fans will still be baffled that Flores can smash the club's transfer record for the third time in seven months and decide Doucoure is surplus to requirements for the rest of the season.
The Hornets invested £5.7m on Etienne Capoue last summer, and topped their biggest-ever fee paid with the £6.1m transfer of Malaga winger Nordin Amrabat last month
The Hornets also announced the signing of Venezuelan forward Adalberto Penaranda, 18, from Udinese, who will remain on loan at Granada.
The French midfielder signed for Watford in a €10.5m from Rennes in January, before being sent out on loan to La Liga side Granada, also owned by Pozzo family,
"He is very much part of Watford's future plans, and in the time between now and pre-season he'll be experiencing high-level competitive football in Spain."
Doucoure suffered a serious knee injury the season after his breakthrough but produced some impressive performances on his return and his good form this campaign has prompted Watford to pursue him once again.
Watford almost signed the France Under-21 international last summer and made their move to land Doucoure to head off interest from Liverpool - who had already lost out tothe Hornets in the chase for Fiorentina midfield anchor Mario Suarez.
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Watford have returned for the 23-year-old after failing with a bid for the France U21 international last August.
France Under-21 international Doucoure has played 80 times for French Ligue 1 side Rennes.
The signings continue the link between Udinese, Granada and Watford, who are owned by the Italian Pozzo family.
Doucoure, 23, will start life on the Pozzo dynasty payroll against Real Madrid - and finish his loan spell with Granada against Barcelona.
The 23-year-old arrived at the club in February and penned a four-year deal - but was immediately sent out on loan to Granada.
The former Rennes midfielder is highly rated in France, and has represented the national team in various youth levels.
At Granada, Doucouré enjoyed regular playing time, and it seems his performances has caught the eye of AS Monaco scouts.
A product of the Rennes youth system, Doucoure made his Ligue 1 debut in the 2012-13 season and has gone on to make 72 first-team appearances, scoring 12 goals.
L’Equipe say the 23-year-old might not consider a departure this summer, as he is keen on playing in the Premier League. The chance of playing in the Premier League is tempting for Doucouré, and that’s the reason he left Rennes in the first place.
Hornets chief executive Scott Duxbury said: "The opportunity to sign Abdoulaye Doucoure now was one we wanted to act upon, given our long-standing interest in the player.
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Gunners boss Arsene Wenger has placed the Nigerian forward top of his shopping list as he looks to strengthen his front line
Doucouré is primarily a defensive midfielder, but could also play in an advanced position. The 23-year-old made 15 league appearances for Granada in the last campaign after joining them in January, and has another four years left on his contract at Watford.
Watford completed a club record £8m deal for Rennes midfielder Abdoulaye Doucoure - and immediately packed him off on loan to Granada.
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Frankly, a €12m is unlikely to tempt Watford into selling Doucouré, and AS Monaco might have to offer to have any chance of completing a deal.
We're delighted here at #watfordfc to announce the signing of Abdoulaye Doucoure from Ligue 1 club Rennes. Welcome! pic.twitter.com/Y6WYjodbzv
Doucouré was heavily involved during pre-season training and could make his debut against Southampton on Saturday. He is definitely one of the players to keep an eye on this season, and could surprise a few.
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Doucouré, Abdoulaye - Watford (ENG)
Watford midfielder Abdoulaye Doucoure could leave Vicarage Road without ever making a Premier League appearance,
Watford's interest in Doucoure comes a couple of days after boss Quique Sanchez Flores admitted he was finding it tough to fit in the 12 players he has already signed this summer.
Doucoure made 15 La Liga appearances during the second half of last season but has now returned to Watford ahead of the new season.
He made his Ligue 1 debut in the 2012-13 season and has gone on to make 57 first-team appearances, scoring 10 goals.
AS Monaco have submitted an offer of €12m to sign Watford’s Abdoulaye Doucouré, reports L’Equipe [print edition] on Friday.
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The Hertfordshire side are currently 10th in the Premier League, five points off a Europa League place.
The 22-year-old, a product of the Rennes youth system, is a France U21 international and was reportedly interesting Chelsea last season.
Doucoure suffered a serious knee injury the season after but produced some impressive performances on his return and was reported to be a target for Jose Mourinho in January.
Watford have also signed goalkeeper Costil Pantilimon, midfielder Mario Suarez and forward Nordin Amrabat during the transfer window.
Instead of forcing out an existing member of Quique Sanchez Flores' squad to meet the maximum permitted quota on foreign players in the Hornets' 25-man Premier League squad, Doucoure will spend four months in La Liga - at Spanish branch of Watford owner Gino Pozzo's family empire.