Stan Wawrinka believes Andy Murray deserves the number one ranking thanks to his consistency over the past year.
Murray has replaced Novak Djokovic atop the rankings heading into the ATP World Tour Finals.
Wawrinka praised the Brit, who like him is a three-time grand slam champion, for his improvement.
"It's amazing what he's doing right now, not only his level, but his consistency and how he keeps winning," the Swiss star said.
"He deserves completely to be number one. I think it's not only about the last 12 months but maybe the last 10 years he's been trying to push more and more to be a better tennis player.
"He's number one and he deserves it."
Wawrinka is excited to see the Murray-Djokovic battle unfold in London, if the pair can reach the semi-finals.
Along with Murray, Kei Nishikori and Marin Cilic, Wawrinka is in the John McEnroe Group, while Djokovic is joined by Milos Raonic, Gael Monfils and Dominic Thiem in the Ivan Lendl Group.
"It's going to be interesting first of all to see first here because he's really close with Novak so it's going to be interesting to see who's going to finish number one," Wawrinka said.
"But he can keep that level for sure."