Speculation has claimed that the 30-year-old has suffered a repeat of an accelerated heartbeat, which kept him out of action for around two months earlier this season.
Despite not confirming the reason for his withdrawal, Fish has targeted a return to the court soon.
"I was reluctant to do so, but am following medical advisement," Fish said in a statement. "I had a good summer and look forward to resuming my tournament schedule in the fall."
Fish had been due to take on Roger Federer this evening.