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There were worrying signs for defending US Open champion Rafael Nadal, who after sealing his place in the fourth round of the tournament with a straight-sets victory against David Nalbandian, collapsed onto the floor, clutching his right leg during the post-match press conference.

It was a grueling encounter against Nalbandian, with the first set alone lasting 62-minutes in a 7-6 (7-5) 6-1 7-5. It should be put in context though that the 25-year-old has played in far more draining encounters.

The Spaniard was talking to the Spanish media afterwards when he fell back on his chair and slid to the floor, clutching his right leg in pain. Medics were summoned and after 15 minutes of treatment, the Spaniard recovered to resume the news conference.

He revealed that it was a cramp, a very painful one, and maintained that he would train as usual on Monday.

It was just cramping in the right leg, in the front and in the back. It was very painful, that's all, he explained. I will train normally on Monday. It was just a normal cramp that could have happened anywhere, but it happened in the press room. Anywhere else, nobody would have noticed.

Afterwards, he posted a video message on his facebook page saying, I had some cramp in the press conference but I am fine, I'm in the hotel having some rest and recovering.

In the fourth round, Nadal will play Luxembourg's Gilles Muller on Tuesday.