The Mexican striker joined Real Madrid in the summer on a season long loan after finding himself surplus to requirements at Old Trafford under Louis van Gaal.
Hernandez initially struggled to make an impact for Los Blancos, but after scoring four goals in last six appearances, he has evolved as a key player, especially in absence of the injured Karim Benzema.
Madrid are now considering the options of signing the 26-year-old permanently, which even a month ago, seemed unlikely.
According to Mexican news channel TDN, Real Madrid’s purchase option to sign Hernandez on a permanent deal expires today, which means the European champions have been forced to ask United for more time.