Three-times champion and world tennis number one Novak Djokovic has been drawn in a group with US Open champion Marin Cilic in next week's season-ending ATP World Tour Finals in London.
Defending champion Djokovic, who's retained his Paris Masters title after beating Milos Raonic, will also face Australian Open champion Stanislas Wawrinka and hard-hitting Czech Tomas Berdych in Group A of the elite event staged at London's o2 Arena.
Cilic is making his debut at the eight-man event.
Second seed Roger Federer, who has won the year-ending tournament six times and who still has hopes of replacing Djokovic on top of the rankings before the end of the year, faces a clash in Group B with home favourite Andy Murray.
Debutants Raonic and Japan's Kei Nishikori, the first Asian-born man to qualify for the showpiece event, complete the group.
Former Wimbledon champion Murray, who won three titles in the past six weeks to secure a place at the tournament after slipping down the rankings, missed last year's tournament because of back surgery.
World number three Rafael Nadal of Spain is missing because of surgery for appendicitis.
Nadal has been released from a clinic in Barcelona after having his appendix removed.
After losing in Basel last month, the 28-year-old world number three announced that his difficult season of injury, illness and worrying defeats, was over and he would be having surgery for appendicitis.
Nadal's aiming to return at the Qatar Open in early January.