The pair will go head to head for a place in the quarter-final in Melbourne, with the Japanese professional stating that he is in "good shape" ahead of the match.
Despite holding a winning 2-1 record over the Spaniard, the 18th seed is expecting a "tough" test on Rod Laver.
"He's always tough to play," said Nishikori. "He gets every ball back and is not easy to beat.
"It's going to be tough, but I have beaten him before. I think I'm in good shape."