Rafael Nadal has questioned the timing of Andy Murray's withdrawal from the US Open after the draw was made last Friday.

Original second seed Murray waited until early Saturday afternoon to decide that his hip was not up to the rigours of a Grand Slam, restricting changes that could be made to seedings in the draw.

Nadal and Roger Federer were left in the same half, meaning that they could face off in the semi-finals rather than final.

Had the Scot withdrawn prior to the draw, the two big rivals could have been kept apart in different halves as numbers one and two.

"I always thought that he was going to be playing if he was here practising, no?" said Nadal in reference to Murray, after beating Dusan Lajovic in the first round.

"It was a little bit strange that he retired just the morning after the draw was made.

"It was something that is a little bit strange and difficult to understand, but the worst thing is he is not healthy and I wish him a very fast recovery."

Murray, who is now back home deciding on his next course of action, explained on Saturday at the time that he intended to play, but felt unable to last the course.

"I was actually practising okay the last few days, but it's too sore for me to win the tournament and ultimately that's what I was here to try and do," he said.

However, Nadal will have to put this thought behind him and focus more on the tournament that lies ahead.

Yet, there is no doubt who Nadal's biggest rival and biggest threat is, fans will be eagerly awaiting the contest between Nadal and Roger Federer, who both look at the top of their game.

Most fans are split down the middle as to who will win this year's US Open, but both champions will be sure to add to their Grand Slam collection this year at Flushing Meadows.