Novak Djokovic's hopes of making a record 19th appearance at the ATP Finals have been dented by a surprise defeat against Jan-Lennard Struff at the Swiss Indoors in Basel.

Playing in the tournament for the first time in 15 years, the 39-year-old lost 6-7 (4-7) 7-5 7-6 (7-5) - the first time he has been beaten by Struff in nine meetings.

"I knew I needed to go for it. There was only one way to play it. So, I was very, very happy," said the world number 27.

"I knew I had to play my best tennis to have a chance. The last eight times he beat me very, very easily. So, I'm very, very happy and pleased with the performance."

The year's top-eight performers qualify for the ATP event in Turin and this result leaves Djokovic - the men's game's record 24-time Grand Slam winner - 11th in the standings.

Djokovic admitted he expected to feel "a little rusty" after his win against Frenchman Ugo Humbert on Wednesday, but now faces a fight to make the finals as he is outside the top 10 for the first time since 2018.

Rafael Jodar holds the final qualifying spot in ninth place, because number one Jannik Sinner is injured and will not take part.

Djokovic is 319 points behind Jodar, although he has the opportunity at the Paris Masters in November to move up the rankings.

The Serb is aiming to move ahead of Roger Federer with his 19th appearance at the finals in Turin. He has won the event a record seven times and has missed the past two editions with injury, but the last time he failed to qualify on merit was in 2017.

Alexander Zverev, Carlos Alcaraz and Ben Shelton have their places confirmed for the showpiece event in Italy from 15-22 November, although American Shelton also surprisingly lost in Basel.

The top seed lost 6-3 6-7 (4-7) 7-6 (7-1) to Swiss wildcard Jerome Kym, who is ranked 222nd in the world.