Novak Djokovic ended his defense of his ATP Finals title before it began by withdrawing from the tournament on Tuesday due to an unspecified injury.

Djokovic, 37, also pulled out of last week's Paris Masters.

"I was really looking forward to being there, but due to ongoing injury I won't be playing next week," Djokovic wrote Tuesday on Instagram. "Apologies to those who were planning to see me."

Djokovic won the tournament for the second straight time last year and seventh time overall by dispatching current top-ranked player Jannik Sinner of Italy in the final, 6-3, 6-3.

Sinner, ironically, prevented the Serbian from claiming his 100th tour-level title with a victory in the final of the Shanghai Masters on Oct. 13.

The season ends for Djokovic without an ATP tournament championship, although he won the gold medal at the Summer Olympics in Paris.

Sinner, Carlos Alcaraz of Spain, Taylor Fritz, Casper Ruud of Norway, Alexander Zverev of Germany, Russians Daniil Medvedev and Andrey Rublev, and Alex De Minaur of Australia will compete in the eight-player tournament in Turin, Italy. The tournament begins on Sunday.

--Field Level Media