With his country's elite World Group status in the balance, Nadal is ready to put his aching limbs on the line just days after beating world number one Novak Djokovic at Flushing Meadows to win his second major of the year.
"We change the surface in a short time and I have just made a big effort but I'm going to do whatever I can to help the team," Nadal told reporters on Wednesday ahead of the tie in Madrid.
"If it is on Friday it would be on Friday, if it is on Saturday, on Saturday, if it is on Sunday, on Sunday. I'm going to try to help with everything within my capabilities."
The Mallorcan's victory in New York capped a stunning year in which he returned from a seven-month injury absence to re-assert himself as a dominant force in the game.
Since re-emerging at a low-key claycourt tournament in Chile in February, the Spaniard has been virtually unstoppable.
Having won the French Open for a record eighth time, Nadal put a disappointing Wimbledon behind him to dominate on the hard courts and move to within four majors of Roger Federer's record haul of 17.
Any thoughts of a relaxing break have had to be put on the backburner, however, as duty calls him back to court to help keep his country in tennis's top tier.
After an under-strength Spain lost to Canada in the Davis Cup first round, they find themselves in unfamiliar territory having only competed in four playoffs in the last 17 years.
Nadal reacted tetchily to suggestions that he could be below par after his recent exertions.
"I've just said it. (I feel) well," he added. "I've got good feelings. What do you want me to say after having winning three tournaments in a row, my feelings couldn't be better."
With home advantage and Nadal's favourite red clay under foot, Spain, whose lineup also includes Tommy Robredo and Fernando Verdasco, should have the edge over a Ukraine team with only one player, Alexandr Dolgopolov, in the world's top 50.
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- Novak Djokovic