Nadal came to London as current world No. 1 but needs to win more matches for ending this season in the top position, as Serbian Djokovic is only 640 points behind him.
"Of course I would love to be the year-ending No. 1," said Nadal at the press conference held in O2 Arena. "But as always, it's not my personal goal. I didn't follow that thing."
Nadal withdrew from last week's Paris Masters due to an abdominal strain, but managed to come to London on Wednesday.
"I started to serve yesterday, very slow," revealed Nadal. "For me the main goal is to be healthy."
The 33-year-old qualified for the season Finals for the 15th consecutive year but is still waiting for his maiden title in the event.
"I am confident that I can be very competitive, but it's a tournament that you will play the top guys since the beginning, so you need to be 100 percent ready," said the 19 Grand Slams winner.
Nadal is in Group Andre Agassi along with Russian Daniil Medvedev, Greek Stefanos Tsitsipas and German Alexander Zverev, while Djokovic is in Group Bjorn Borg along with Roger Federer, Dominic Thiem from Austria and Italian Matteo Berrettini.
Nadal will play against defending champion Zverev in his opening match on Monday.
( With inputs from IANS )