The 25-year-old, who had a season-long loan in La Liga with Real Mallorca last term, rejoined the Baggies for pre-season training at the beginning of the month.

But he expressed his desire to return to Spain for professional and family reasons and Albion initially rejected an offer from Sevilla last month for Valero, the club's £4.7million record signing when he arrived two summers ago.

However, after lengthy negotiations they have agreed to his move to Villarreal and sporting and technical director Dan Ashworth said: "After relegation in 2009 we agreed to loan Borja to Real Mallorca.

"On the back of an outstanding season in Spain and taking into account his professional and personal wishes, we decided to accept an offer from Villarreal.

"I'd like to thank Borja for his contribution and his professional attitude throughout the last two years. We wish him well over the coming season."

PA Sport