The Mexico international moved to Los Blancos on loan towards the end of the transfer window, and said that he had no plans to warm the bench at Santiago Bernabeu.
"No-one trains to be a back-up," Hernandez told Neox TV. "I'm a football player and there are 11 starters, so the ones on the outside are always waiting for a chance and no player will say that they train to wait on the outside.
"I know I will have to face Karim Benzema, as happened to me when I arrived at Manchester. It is normal to compete for a spot.
Hernandez joined United in 2010.