The two sides meet for the first time in the top flight on Sunday at the Cardiff City Stadium.
Hernandez, who recently returned to action following a lengthy spell on the sidelines with a knee injury, believes that the match between the local rivals will be tightly contested.
"This game is very important for the club and most important for the fans," he told the South Wales Evening Post.
"It's a difficult game because both teams want to win the match for the fans and the occasion should be unbelievable."
Swansea are currently in ninth place in the Premier League table, while Cardiff sit in 16th spot.