American John Isner will take Nadal's place in the eight-man season finale in London.
LONDON — Rafael Nadal has pulled out of the season-ending ATP Finals because of an abdominal injury.
Nadal announced Monday on Twitter that he is done for the year, citing the same stomach muscle issue that forced him to withdraw from last week's Paris Masters.
He added that he also would have surgery on his right ankle so he can start 2019 healthy. Nadal hasn't competed since he retired from his U.S. Open semifinal because of a painful right knee.
He lost his No. 1 ranking to Novak Djokovic on Monday.
The 32-year-old Spaniard ends 2018 with a 45-4 record and five titles, including his 17th Grand Slam trophy at the French Open in June.
The ATP Finals for the top eight players in the men's rankings are next week.