Watford have sold left-back Pervis Estupinan to Villarreal for an initial fee of around £15m.
The Ecuador international, 22, arrived at Vicarage Road from LDU Quito in his home country in 2016 but has never played a game for the Hornets.
Estupinan spent last season in LaLiga on loan at Osasuna and was with Granada, Almeria and Mallorca before that.
Earlier this year Manchester United were linked with a €7m swoop for the player, with Ecuadorian outlet Expreso reporting that Atletico Madrid were also particularly keen.
United’s idea was to buy him and loan him out to another English side, as they wait for him to get up to speed in the Premier League.
However, a deal never materialised and he is now returning to Spain on a permanent basis with his commitment questioned.
Watford’s chairman and CEO Scott Duxbury said: “As (head coach) Vladimir (Ivic) has said repeatedly over the past week or so, having a squad of players 100 per cent committed to our challenge is imperative.
“Continued player trading – incoming as well as outgoing – is inevitable over the course of the next month or so, given the shortened pre-season timescales this summer.
“But that doesn’t mean our focus will be distracted. Building a fully-committed squad of players is of the utmost importance.”