The 23 year-old has quickly became a United target in these last few days of the transfer window with the Red Devils having not much success in their search for a top drawer signing with negotiations for Everton's Felliani heading to a deadlock.
United's first bid was rejected as his release clause is 36 million euros but the with the interest they've received from Herrera, they will probably look to break the release clause with a bigger bid.
Athletic Bilbao have a history of playing it tough when it comes to selling their players with Javi Martinez only leaving for the release clause while others like Llorente and Amorebieta ran their contracts down despite wanting to leave much earlier.