Nadal, who beat Ivan Dodig earlier today, admitted that he watched some of the Australian's victory.
"I watched a lot of moments of the match, my feeling is that Hewitt played great," Nadal told reporters.
"I was happy for Leyton, he's a great fighter. [The fact he is] still on tour with the motivation to keep playing, keep fighting, is something I admire a lot.
"My motivation is to keep playing for a long time. I don't know [if it will be] three, four, five, six years. I don't know, I go day-by-day."
Nadal faces Philipp Kohlschreiber in round four.