Stefanos Tsitsipas has withdrawn from the ATP Finals due to an elbow injury, organisers announced on Wednesday with the Greek having lost his opening match against Andrey Rublev.
Tsitsipas, who won the event in 2019, lost 6-4 6-4 to the Russian in his Green Group match on Monday and was due to face Casper Ruud in his next encounter.
However, the ATP said that the Greek world number four had suffered a right elbow injury and would play no further part in the tournament in Turin.
British world number 12 Cameron Norrie will replace Tsitsipas, who has been carrying the injury since retiring from the second round of the Paris Masters earlier this month.
The withdrawal follows that of Matteo Berrettini on Tuesday after the Italian suffered an abdominal injury in his opening match against Alexander Zverev. He was replaced by compatriot Jannick Sinner.