Novak Djokovic can take the first step towards regaining the world number one ranking when he opens his title defence at the ATP World Tour Finals on Sunday.
Djokovic could reclaim the top ranking from Britain’s Andy Murray with another successful week at London’s O2 Arena.
“It’s one of the things that we’re all fighting for here, let’s see where it takes us,” Djokovic told BBC Sport.
“Being number one in the world, in a season like this, is of course the pinnacle of the sport next to winning a Grand Slam.”
The top eight singles players and doubles teams are divided into two groups of four at the ATP World Tour Finals, with the top two from each group progressing to the semi-finals.
Briton Jamie Murray and Brazil’s Bruno Soares take on Treat Huey and Max Mirnyi in the evening session at 18:00, followed by Wimbledon finalist Milos Raonic against Gael Monfils.
For the first time since the season-ending finale moved to London in 2009, neither Roger Federer nor Rafael Nadal will be present as both ended their seasons early to recover from injuries.