Novak Djokovic won't defend his ATP Finals title after ruling himself out Tuesday citing an injury, leaving the season-ending event without a member of the Big Three of men's tennis for the first time in 23 years.

Novak Djokovic won't defend his ATP Finals title after ruling himself out 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.