Nadal returned to the court for the first time since Wimbledon last week in Beijing before he was diagnosed with appendicitis ahead of the Shanghai Masters.
He was able to play his second-round opening match against Spanish compatriot Feliciano Lopez on Wednesday but lost before returning to Spain for tests in Barcelona.
Nadal said after his Shanghai exit he was planning to play the indoor hard court tournament in Basel later this month as well as the Paris Masters and the season-ending ATP Tour Finals in London.
The 28-year-old will then have surgery to remove his appendix and hopes to be back in time for the beginning of the 2015 season.
After Nadal's early exit in Shanghai, Swiss Roger Federer will replace him at number two in the rankings when they're updated next week.