Madrid:Rafael Nadal "is worried" about his constant injuries although the former top-ranked player is confident of getting back to his best form, according to Spain's Davis Cup captain Albert Costa.
"He is worried about his physical state but he's working every day to get better," Costa said on Wednesday.
Nadal is sidelined for Spain's Davis Cup series against Switzerland next week after another serious knee injury forced him out of the Australian Open in January.
Nadal has been plagued by injuries since November 2008, when knee tendinitis forced him to miss Spain's Davis Cup win over Argentina. The 23-year-old Nadal missed several months last summer to knee problems after the French Open, where he failed to lift the trophy for the first time in five years.
"Until last year at Roland Garros and the problems, he had achieved everything," Costa said. "It's normal, after 22 years and winning everything, to have some down time."
Four-time Grand Slam winner Manolo Santana believed Nadal would recover and would be back at his best by Indian Wells, where he won last year.
Nadal recovered to help Spain win a second straight Davis Cup in December, although he and top-ranked Roger Federer will both be missing from the March 5-7 best-of-five series.
Costa said there is "no limit" to his team even if it has a different makeup then usual with Nadal and Fernando Verdasco sidelined to injury, and Feliciano Lopez left out.
"That was my decision, that was a technical decision," Costa said. "I think (the others) also deserve a chance to represent Spain. You have to have alternatives so you're ready for any future tie also."
Former top-ranked player Juan Carlos Ferrero, David Ferrer, Tommy Robredo and Marcel Granollers will play at the 11,000-capacity bullring in the northern city of Logrono.