Jannik Sinner and Carlos Alcaraz are poised to add another entry into their rapidly developing rivalry when the ATP Finals open Sunday without any members of the Big Three for the first time in nearly a quarter century.

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.

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.”