The defending champion was speaking to reporters after his third round win over David Nalbandian when he suddenly stopped talking, then covered his face with his hands and slumped to the floor.
Journalists were ordered to leave the room and the lights were turned down as medical staff were called to treat the Spaniard, who slid from his chair on to the floor.
He was obscured by a desk but closed circuit television showed a trainer massaging his right leg while another man gave Nadal ice and fluids. Nadal remained on the carpet for about 10 minutes before he was eventually helped to his feet.
Image: Rafael Nadal of Spain reacts to pain during a press conference after his match against David Nalbandian of Argentina during the U.S. Open tennis tournament in New York, Sunday, Sept. 4, 2011. Answering questions in Spanish, Nadal suddenly started grimacing in pain. He tilted his head back, covered his face with his arm. After a few nervous moments, Nadal popped back up. A simple leg cramp, he insisted.