The Spaniard was speaking after Djokovic was knocked out in the second round of the Madrid Open on Wednesday.
Nadal has enjoyed his own resurgence over the past 12 months, having reclaimed the world number one spot and clinched two more major titles.
Britain's Kyle Edmund enjoyed one of the biggest triumphs of his career by defeating Djokovic 6-3 2-6 6-3.
Elsewhere, Kevin Anderson thundered down 25 aces in his victory over Mikhail Kukushkin, while there were also wins for Philipp Kohlschreiber, David Goffin and John Isner.
Seventh-seeded John Isner beat fellow American Ryan Harrison 7-6 (1), 7-6 (7), while eighth-ranked Kevin Anderson defeated qualifier Mikhail Kukushkin 5-7, 7-6 (3), 6-2 to set up a third-round match against Philipp Kohlschreiber, who beat Roberto Bautista Agut 6-3, 4-6, 7-5.
Serbia's Novak Djokovic in action against Kei Nishikori of Japan during their first round match of the 2018 Mutua Madrid Open tennis tournament at Caja Magica in Madrid, Spain, 07 May 2018. I couldn't ask for a better start. "It's time to try and beat these guys and I was pleased how I managed my game". "It's not nice to see that you're falling down in the rankings, that you're not feeling as good as you're used to feeling, because he's always been really fit". Djokovic was tough and David is a top player so it's very pleasing'. I'm having a good year, but nothing's ideal.More news: Everton must offload players to make room for quality - Allardyce
The Serb's disappointing year continued as he slumped to a 3-6, 6-2, 3-6 defeat. The 12-time Grand Slam champion has an uninspiring 6-6 win-loss record in the ongoing season. Although the Serb did look mightily impressive in round one, I suspect he may have a hard time backing up that kind of supreme performance.
The unseeded British player then broke Djokovic's serve to go up 5-3 and easily closed out the match on his serve.
'He has improved his backhand, ' he said. "I feel much better about everything that is happening on the court and around tennis, in general, with my body than maybe two months ago".
KYLE EDMUND celebrated finally overcoming a "legend of the game" yesterday after beating Novak Djokovic, and then admitted it was about time he started beating the game's greatest players. I tried but obviously, yeah, wasn't to be today.
"It's not the end of the world", Djokovic said. Obviously, I've played this sport so many years and had a bunch of success. "I just knew that if I put myself in the match hopefully in the closing stages I would give myself a chance".