David Ferrer found
Novak Djokovic the player that makes him feel most uncomfortable during a match despite beating him a handful of times.
Ferrer played many times against Djokovic during his tenure on the Tour and for him, the Serbian was the toughest opponent to face. He said it in an interview with El Mundo where he also touched upon never beating Federer for example:
"This depends on the characteristics of each player. I never beat Federer, but for me the feeling was that when Djokovic was good he was the one who made me feel most uncomfortable because he couldn't hurt him with any of my punches."
Ferrer went 0-17 against Federer and 5-16 against Djokovic despite not feeling as great when playing the Serbian. Djokovic is a tremendous all-round player and his defensive capabilities gave Ferrer a lot of problems because he was never the biggest hitter on the tour.
He went as far as to say:
"And from the way I played, I had the feeling that when he was fine he couldn't even beat him in one game," he added.