Valero has long been linked with a move to Spain after impressing on loan with Real Mallorca last season.
“There have been lots of rumours in the media over the past few weeks about Sevilla being interested in Borja but the bid they tabled yesterday was the first we have received from them,” sporting and technical director Dan Ashworth told West Brom’s official website.
“It was rejected out of hand as it was nowhere near what we would regard as an acceptable offer.
“Borja enjoyed an outstanding season in Spain and we have just been promoted to the top flight.
“If we do not receive a satisfactory offer for Borja, we are more than happy for him to rejoin us for pre-season training in three weeks’ time and be a part of our Barclays Premier League squad.”