Rafael Nadal of Spain poses with his trophy after winning the men's singles final match against Novak Djokovic of Serbia at the US Open tennis tournament in New York's Central Park, Sept 10, 2013. [Photo/Agencies]

MADRID - Playing the Davis Cup on clay in Madrid this week is not ideal preparation for the hard-court swing in Asia and an assault on the number one ranking, according to newly crowned US Open champion Rafa Nadal.

Spaniard Nadal, currently number two behind Novak Djokovic, is poised to replace the Serb as the world's top-ranked player after he beat him in Monday's final at Flushing Meadows.

Before he travels to Asia, Nadal will return to Davis Cup action for the first time since 2011 to help Spain in their World Group playoff at home to Ukraine starting on Friday.

"Given the fatigue I am feeling, what I would like to do is rest and recuperate well physically and mentally for the Asian tour," Nadal said in an interview published in Spanish sports daily Marca on Wednesday.

"It's the final sprint of the year and I am fighting for something as special as finishing as number one," added the 27-year-old, who last held the top ranking in June 2011 and slipped to five before his return from injury in February.

"The Davis Cup won't help me in that goal because to be prepared for what I have left it's not good to change surfaces.

"But I said I would go already a few months ago, I committed myself and I will be in Madrid.

"I feel duty bound to go to Madrid and I feel duty bound to help the team so we stay in the World Group.

"I believe Spain deserves to be among best for what it represents and has represented in the world of tennis for so many years."

Spain's Davis Cup captain Alex Corretja said he would wait and see what state Nadal was in when he arrived in the capital on Wednesday before deciding whether he should feature in Friday's opening singles.

He may opt to rest him and play in-form Tommy Robredo and Fernando Verdasco, keeping his best player in reserve for Saturday's doubles or Sunday's reverse singles in case the unfancied Ukrainians spring a surprise.

"More than swamped, right now I feel empty, a little tired of everything," Nadal told Marca.

"In emotional terms, when you have been playing for a month and winning all your matches and then you put the cherry on the cake here you have a slump and that's logical.

"It's nothing strange and I hope to be fine in a few days."

Spain are in the Davis Cup playoffs after losing away to Milos Raonic's Canada in the first round in February.