Djokovic has played in only two events since his disappointing third-round exit from the US Open. He reached the final of the Shanghai Masters but was defeated by Jannik Sinner, before losing against the Italian again in the Six Kings Slam.

BELGRADE, Serbia (AP) — Novak Djokovic won’t defend his ATP Finals title after ruling himself out on Tuesday due to an unspecified injury. Djokovic wrote in an Instagram story, “I was really looking forward to being there, but due to ongoing injury I won’t be playing next week. Apologies to those who were planning to see me.”

Djokovic has won the ATP Finals, which is the end of year tournament somewhat seen as a fifth major, a record seven times. He won the title last year, beating current World No. 1 Jannik Sinner.