Djokovic faces Spaniard Roberto Bautista Agut in the last-16 of the Italian Open on Thursday.
Earlier late on Tuesday, defending champion Andy Murray was eliminated after losing 6-2, 6-4 to Fabio Fognini in a second round match.
"I know that I am in the minority", said Petchey.
"But a year ago I found some emptiness for the first time in my life in terms of motivation. I mean, he had a lot of matches played at the beginning of the year, and he did amazingly well". "And this year it's the same".
Third seed Stan Wawrinka avenged his defeat by unpredictable Frenchman Benoit Paire in Madrid last week when the 2015 French Open champion won a topsy-turvy match 6-3 1-6 6-3.
The Japanese will next meet Aregntine Juan Martin Del Potro who beat British Kyle Edmund five and four.
"The stadium will be very loud for him". I am very proud and humbled by the achievement.
Nadal went over to Almagro's side of the net to ask what was wrong and consoled his opponent. "But at the same time, it's so hard to be on the top of your game and mentality for every week", Nadal said. "He felt something on the knee".
Nadal though was distressed to see Almagro injured who he also helped from the court.
Nadal has won all three clay competitions this season while Murray struggled in Madrid and Monte Carlo and lost out in the semi-finals in Barcelona.
Federer pulled out of the French Open, starting May 28. Almagro immediately retired, giving Nadal a safe passage into the last 16, where he will play either Jack Sock or Jiri Vesely.
Petchey was certain in his belief that Maria Sharapova was harshly treated in not being awarded a French Open wildcard by the French Tennis Federation following her return from a 15-month doping ban.
Spaniard Muguruza, the third seed, will need to sharpen up though after enduring a awful start against 50th ranked teenager Ostapenko before the reigning French Open champion flicked the switch and won 2-6 6-2 6-1.
"No words, games, or actions will ever stop me from reaching my own dreams".
"What worries me is trying to be healthy, try to be competitive, and the most important thing is be happy".