Hernandez, 34, joined Leeds permanently in 2017 and is due to sample his first experience of a Leeds versus United match in their pre-season friendly in Perth on Wednesday.
Hernandez was roommates with Juan Mata during their time together at Valencia and has already spoken to his compatriot about this week's encounter. Hernandez has a particularly fond memory of his first trip to Manchester.
"Yesterday when I arrived here (Perth), I text him and he text me: 'See you Wednesday'," Hernandez added. "He told me he wants my shirt and I want his shirt, I have a lot of his shirts but I want the new one. He was my teammate for four years in Valencia and my roommate and I am happy to play against him.
"The best memory for me is I played in the Champions League with Valencia and we played in Manchester United's stadium, Old Trafford. We drew 1-1 and I scored the goal. It was special for me because I am the only one in Valencia to score in this stadium."