The world record holder and gold medal favourite struggled through only as the last qualifier from his race.
Robles, renowned for his smooth style, clumsily hit the opening hurdle and trailed most of the race before his natural speed brought him back into contention.
He qualified behind Maurice Wignall of Jamaica and Helge Schwarzer of Germany in 13.67 seconds, .76 off his world record time.
After the race, he said an injury over the winter was acting up again. It did not affect his results during the summer, winning his nine races coming into the championships.
"I feel pain in my left thigh," Robles said. "I don’t know what’s going on. I thought it was only a small problem but now I know that I really have a problem.
"I cannot say that I’ll continue to run or not. I’ll talk with the physiotherapist and doctor, and we’ll see.
"I promised Fidel Castro to bring home the gold medal for him and I want to keep my promise. I am a warrior and I will fight."
Rival Liu Xiang of China is not competing in Berlin because of a longstanding injury.