The 18-year-old is yet to make an appearance for the Hornets after arriving at the club in July 2017 but the player has impressed in the Spanish Segunda Division with SD Huesca on his loan spell.
Reports have suggested La Liga giants Barcelona were interested in making a move for the youngster in the January window but the deadline came and went without incident.
However, Watford are believed to have now put a 25m euros price-tag on the highly-rated forward, who has scored 11 goals in 24 appearances with Huesca this season.
Uwe Rosler was sacked by Fleetwood following a 3-0 reverse at Doncaster which condemned Town to a seventh straight defeat in all competitions.
Cambridge interim head coach Joe Dunne was pleased with how his side adapted to beat Grimsby 3-1.