Ander Herrera has agreed to personal terms with Manchester United, who are set to pay his release clause of $49 million. The release clause increases to $54.4 million on July 1.
Herrera is one of the world's best central midfielders and won't turn 25 until August.
Herrera has been at Athletic Bilbao since his 2011 move from Zaragoza.
United offered £24 million for Herrera last August, but it was rejected by Athletic Bilbao.