The defending champion was speaking to reporters after his third round win over David Nalbandian when he suddenly stopped talking, covered his face with his hands and slowly slid off his chair and on to the floor behind a desk.
Journalists were ordered to leave the room and the lights were turned down as medical staff were called in to treat the Spaniard. A trainer massaged his right leg while another man gave Nadal ice and fluids.
Nadal remained on the floor for about 10 minutes before he was eventually helped to his feet. He returned to the conference room shortly after to explain what happened.
"I just have cramping in my leg, that's all," he said. "(It as) in front, in back. It was so painful, that's all."
Nadal had just beaten Nalbandian 7-6 6-1 7-5 on a baking hot day at Flushing Meadows
