Argentina’s Juan Martin del Potro withdrew from the season-ending ATP Finals in London and will be replaced by Japan’s Kei Nishikori due to a right knee injury he sustained in Shanghai last month.

Del Potro, who reached a career-high ranking of No.3 earlier this season, continues his rehabilitation following an injury sustained while competing at the Rolex Shanghai Masters in October but is unable to recover full fitness ahead of London. The world number four last played in the tournament in 2013.

Nishikori will join Novak Djokovic, Rafael Nadal, Roger Federer, Alexander Zverev, Kevin Anderson, Marin Cilic and Dominic Thiem at the event.

“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. Of course, it’s disappointing for me right now, but I had a very good season overall.”

28-year-old Nishikori makes his fourth appearance at the season finale, having reached the semi-finals at the Nitto ATP Finals on two occasions, his debut in 2014 and in 2016 losing out to Novak Djokovic both times. The Japanese star is only the third player since 1994 to have won an ATP Challenger Tour title and qualified for the Nitto ATP Finals in the same season, following in the footsteps of Ivan Ljubicic who won in 2005 and Robin Soderling in 2009.

The ATP Finals run at the O2 Arena from 11-18 November.