The 24-year-old has been involved in a whirlwind round of public events and television appearances since capturing his maiden U.S. Open title by beating Serb Novak Djokovic in Monday's final.
Nadal, though, said he could not be classified as Spain's all-time greatest sportsman despite adding the season's final tennis grand slam to his five French Opens, two Wimbledons and one Australian Open championship.
"I think it's obvious I'm not," the left-hander said in an early-morning news conference at Madrid airport after his overnight trans-Atlantic flight from New York.
"It would be tremendously arrogant of me. All athletes have their merits for what they have done in their particular sports."
World number one Nadal continued to display typical modesty when he apologised to reporters for the early news conference.
"I'm very grateful. I know it's a difficult time of day. I'm sorry," said the Spaniard, grinning from ear to ear and showing little sign of jetlag.
Nadal also explained the improved serve that surprised many pundits at Flushing Meadows.
"The truth is I was not serving very well in the tournaments leading up to the U.S. Open," he said.
"I've worked hard on the service because it needed it. I decided to change my grip two days before the tournament, to make it (the ball travel) quicker especially when serving against the wind there always is on centre court at Flushing Meadows.
"It was a risk but I had to take it and it all worked out pretty well."
Nadal will now take a break from tennis and the Real Mallorca shareholder and football fan is planning to watch Real Madrid later on Wednesday.
He will be at the Bernabeu to see the self-proclaimed Portuguese 'Special One' Jose Mourinho's new team take on Ajax Amsterdam in their Champions League opener.
