"I have been dealing with all my injuries in the past, and now it's time to take care of my body, see what the MRI says or what the doctor says".
"I have a tough match against Grigor and know I will have to play my best. but I am playing well".
Nadal saved a break point at 2-2 in the decider, and is still to lose his serve in Shanghai, before breaking serve in the next game and going on to win to set up a semi-final clash with Marin Cilic.
Del Potro received lengthy treatment to the area - which has undergone surgery in the past - before battling through 4-6 6-1 6-4.
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The next couple of games went past within a blink of an eye, and Harrison soon found himself serving for the set at 5-3 up. The world number two claimed two more breaks in the next to seal the deal in an hour and 18 minutes.
The Spaniard, 31, breezed through the first set but was unable to break Dimitrov in the second, and the Bulgarian was strong in the tie-break to force a deciding set.
Federer, the second seed, has not dropped a set all week. Consolidating the break of serve, the world number nine had the golden opportunity to extend his lead when he earned a break point in the third game with Harrison unable to gain any rhythm on his serve.
Breaking serve for the second straight time, Harrison looked well on course for the huge upset in the lovely city of Shanghai.
Earlier in the afternoon, fourth seed Cilic knocked out Albert Ramos-Vinolas with a straightforward 6-3, 6-4 victory.