Nadal has recently returned from a wrist injury, but with surgery required for appendicitis before the start of next season, the Spaniard has admitted that he hasn't made a decision on whether to compete at the O2 Arena.
The 28-year-old told Sky Sports News: "I have had weeks of injury so it was not been an easy season for me. At the end, I have to do the surgery but I have to find the right moment.
"I need to see how things go and how my body accepts the antibiotics, so after all the things that have happened over the last few weeks - let's see.
"I will try to do my best to make London but I cannot say. I do not know 100%."
Nadal has suffered defeats in his last two matches, with Martin Klizan beating him in three sets in Beijing before Feliciano Lopez registered a straight-sets triumph over the 14-time major winner in the second round of the Shanghai Masters.