British number one Cameron Norrie has earned the chance to compete at the ATP Finals after Stefanos Tsitsipas's withdrawal.
The 26-year-old initially missed out on a place at the tournament after his third-round elimination in the Paris Masters but was one of two alternates alongside Jannik Sinner.
Sinner is already involved after replacing Matteo Berrettini earlier this week, and the ATP have now confirmed that world number four Tsitsipas is out due to an elbow injury.
The Greek had already lost to Russia's Andrey Rublev before withdrawing, and Indian Wells Masters champion Norrie kicks off his ATP Finals bid against Norway's Casper Ruud at 8pm tonight.
The Brit will then face Novak Djokovic in Friday's Green Group fixture, with seven players aspiring to join Daniil Medvedev in the semi-finals.
Norrie's compatriots Joe Salisbury and Jamie Murray are enduring mixed fortunes in their respective doubles bids, with Salisbury and Rajeev Ram already beating Murray and Bruno Soares, who have suffered two defeats from two in the tournament.
