Nadal complained about the length of the ATP Tour before Shanghai
Top seed Rafael Nadal advanced to the semi-finals of the Shanghai Masters after Ivan Ljubicic retired with a thigh injury with the score at 3-6 6-3.
Croatian Ljubicic is the eighth player to withdraw, while world one Roger Federer and world number three Andy Murray skipped the event altogether.
Nadal next plays fellow Spaniard Feliciano Lopez, who beat Sweden's Robin Soderling 7-5 (7-4) 6-3.
Number two seed Novak Djokovic beat Frenchman Gilles Simon 6-3 2-6 6-2.
The Serb will meet number six seed Nikolay Davydenko in the last four after the Russian defeated Radek Stepanek of the Czech Republic 6-1 4-6 6-1.
Ljubicic took the first set of his quarter-final against world number two Nadal, a single break, courtesy of a Nadal forehand error, the deciding factor.
The world number seven had the chance to break at 1-1 in the second, but Nadal saved four break points and broke Ljubicic to love in the next game.
Nadal held his nerve to claim the set, but by then Ljubicic's discomfort had become obvious and he was unable to come out for the third.
"It was tough, it was a difficult match," said Nadal. "I'm sorry for him, it's not very nice to win like this. I just wish him a fast recovery."
Djokovic also had an uncomfortable day, needing two breaks to overcome stubborn Simon in the first set.
The Frenchman's dogged defence saw a frustrated Djokovic go to pieces in the second as he produced a host of unforced errors.
And in the third, Djokovic was a model of inconsistency, throwing in some misjudged drop shots and double faults and blowing his early break.
Djokovic broke again immediately, but put a routine overhead into the net to allow Simon to break back before smashing his racquet in annoyance.
Again Djokovic broke with the help of a trademark drive volley and this time he was able to make his advantage stick, holding for the first time in the set before going on to claim victory.
"You know, it's crazy, it was kind of advantage for the return player today," said Djokovic, referring to the slowness of the court.
"But most of the time when I smash the racquet things go better from then on."