Nadal collapses at US Open press conference

Nadal, 25, was talking to the media, two hours after his third round win over close friend David Nalbandian, when he grimaced in pain, screwed up his eyes and slumped in the back of his chair, feeling his right leg.

The world number two, a winner of 10 Grand Slam titles, slipped to the floor while tournament medical staff were summoned.

Scores of reporters and camera crews were ushered out of the packed interview room deep inside the Arthur Ashe Stadium.

However, after 15 minutes of treatment, Nadal was back on his feet, insisting that the problem was merely cramping.

"It was just cramping in the right leg, in the front and in the back. It was very painful, that's all," said Nadal, who resumed his news conference standing instead of sitting.

A smiling Nadal said the incident will not affect his preparations for his fourth round match against Luxembourg's Gilles Muller, scheduled for Tuesday.