Celtic manager Ronny Deila insists Virgil van Dijk does not want to leave the Scottish Premiership leaders in January.
Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
The Spanish club, also owned by Watford supremos the Pozzo family, confirmed on their website that Iriney has agreed a season-long deal at Vicarage Road.
The 32-year-old has spent more than 10 years in Spain and also played for Rayo Vallecano, Celta Vigo, Real Betis and Almeria.
Watford caused controversy last season by bringing in a host of loanees from Granada and the other Pozzo-owned club, Udinese.