Stefanos Tsitsipas withdraws from ATP Finals due to back injury.
Stefanos Tsitsipas has withdrawn from the ATP Finals after retiring with injury against Denmark's Holger Rune on Tuesday.
Tsitsipas, 25, trailed 2-1 in his Green Group match and after consulting with a doctor at the changeover pulled out.
The Greek world number six appeared to be troubled by a back problem and left the court to a few jeers from the crowd inside Pala Alpitour in Turin, Italy.
"It kills me not to be able to finish this tournament," Tsitsipas said.
"I'm really gutted that I wasn't able to finish the match. It's a shame also not to give that spot to someone else to at least try and do something with it.
"Unfortunately, I felt terrible on the court. I did what I could do in the best possible way to be ready and fit for this match, but it didn't work out for me."
His withdrawal from the tournament means number one alternate Hubert Hurkacz will replace him for his final match against Novak Djokovic.
"For sure it was very unfortunate," 20-year-old Rune said. "Even in the first service game you could see he wasn't serving anywhere near full like he can, I knew something was off."
Djokovic is now able to book his spot in the last four with a win over Jannik Sinner later on Tuesday.