Athletic chiarman Josu Urrutia confirmed on Friday that he has rebuffed a bid from David Moyes' side, who have so far floundered in their attempts to attract midfield reinforcements to Old Trafford.
Ander's release clause stands at €36m, and Athletic have told the Premier League champions that they must match that figure if they want to sign the 24-year-old.
The Basque club last summer insisted that Bayern Munich pay the full clause for Javi Martinez, who eventually moved to Bavaria for €40m.
It is unknown whether United will return with a larger offer for the midfielder, who joined Athletic from Zaragoza in 2011, though manager Moyes is a long-time admirer.
