Kei Nishikori is happy to see Andy Murray replace Novak Djokovic as world number one, but lauded the Serbian for his achievements.
The Brit enters the ATP World Tour Finals as the world's top-ranked player, ending Djokovic's 122-week stay as number one.
Nishikori welcomed the change at the top, saying Wimbledon champion Murray deserves his spot.
"He's having a great year so far, number one player, that's great to see, a new number one player," he said.
"What Novak did these last couple of years is something nobody did before but I think this is a great change."
However, Nishikori – who will face Murray, Stan Wawrinka and Marin Cilic in the John McEnroe Group in the Finals – refuses to write off Djokovic.
He believes the Serbian 12-time grand slam champion will still be hard to beat.
"I think there is a chance for Novak to be number one again at the end of this year," Nishikori said.
"What he's done these couple of years has been amazing, he's not going to lose his tennis, his confidence.
"In these last few months maybe he's not having the best few months but this is a great tournament, great atmosphere and I'm sure he's going to play his best next week."
The Ivan Lendl Group at the Finals includes Djokovic, Milos Raonic, Gael Monfils and Dominic Thiem.