Novak Djokovic will not play at the ATP Finals in Turin because of injury.
The Serbian won a record seventh title at the season-ending event last year by beating Jannik Sinner in the final and will miss it for only the second time since making his debut in 2007.
Djokovic's only previous absence came in 2017 after he cut short his season because of an elbow injury.
He last appeared on court at the lucrative Six Kings Slam in Saudi Arabia last month, where he lost to Sinner before beating Rafael Nadal.
Djokovic subsequently pulled out of last week's Paris Masters and, writing on Instagram, he said: "It's quite an honor to qualify for the nittoatpfinals in Turin.
"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. Wishing all the players a great tournament. See you soon!"
Djokovic withdrawal means he ends his season having won only one title - a long-coveted Olympic gold medal in Paris - while he has contested just 11 tournaments.
He admitted seeing big rivals Nadal and Andy Murray follow Roger Federer into retirement was difficult for him but insisted he is still motivated to continue chasing the biggest titles.
The 37-year-old will be outside the top four seeds for the Australian Open in January, with his ranking currently six but likely to fall further.
Djokovic's withdrawal means Casper Ruud, Alex De Minaur and Andrey Rublev will join Sinner, Carlos Alcaraz, Alexander Zverev, Daniil Medvedev and Taylor Fritz in Italy for the tournament beginning on Sunday.
