London - Kei Nishikori will compete in the ATP Finals in London following the withdrawal of Juan Martin del Potro due to a right knee injury.
The Japanese player joins Novak Djokovic, Rafael Nadal, Roger Federer, Alexander Zverev, Kevin Anderson, Marin Cilic and Dominic Thiem at the elite eight-player event, which starts on November 11.
Del Potro, who reached a career-high ranking of number three earlier this season, injured his knee while competing at the Shanghai Masters last month.
"It's frustrating for me not to be able to compete in London," said Del Potro.
"It's a very special tournament and I've tried everything possible to get my knee better. The rehabilitation is making good progress but I need more time."
Nishikori, 28, will be making his fourth appearance at the season finale, having reached the semi-finals in 2014 and 2016.