The 27-year-old was deemed surplus to requirements by United boss Louis van Gaal and allowed to spend the whole of last term on loan at the Bernabeu.
Hernandez initially struggled for game time at Madrid, but came to the fore at the end of the season and looked to have done enough to win a permanent move to the Spanish capital.
However, the departure of coach Carlo Ancelotti has left his future in limbo and he admits he doesn't have a clue what his next step will be.
"Of couse it's in my head because it's my future," he told Reuters. "I do not know where I will go, United, Madrid or anywhere. I'm just enjoying my holiday for now.
"Ancelotti was my coach but now Benitez is there. He doesn't have to speak to me because I was on loan from Man United.
"But I am very calm because, thankfully, the last two months at Madrid were very good and showed a lot of things. That gave me a lot of confidence for my future.
"I think that Rafa knows me. He is a really good coach and I think he will do a great job at Madrid."