Sydney - A Grigor Dimitrov-led Bulgaria was among the final six teams announced on Thursday for the ATP Cup in Australia - the new world tennis team event.
Chile, Poland, Uruguay, Moldova and Norway were the other countries to make the grade, based on the ranking of their number one singles player at the second entry deadline of November 13.
The rest of the 24-nation field was announced in September, although Switzerland later pulled out after Roger Federer opted to skip the tournament.
The field will be split into six groups across Sydney, Brisbane and Perth.
As the highest-qualifying country at the second deadline, Bulgaria replace the Swiss and join Belgium and the Andy Murray-led Great Britain in Group C in Sydney.
The championship takes place from January 3-12 in the lead-up to the year's first Grand Slam, the Australian Open in Melbourne.
World No 2 Novak Djokovic will begin his 2020 season representing Serbia with Dusan Lajovic in Brisbane, against France, South Africa and Chile.
World No 1 Spain's Rafael Nadal will kick off his campaign in Perth alongside Roberto Bautista Agut facing Japan, Georgia and Uruguay.
Eight teams - with up to five players each - will emerge from the round-robin stage to compete in the knockout phase in Sydney until one is left standing with ties comprising two singles and one doubles match.
Most of the world's top 30, minus Federer, are taking part.
The new-look start to the year offers A$22 million in prize money and a maximum of 750 singles and 250 doubles ATP rankings points.
It will be held on the back of a revamped Davis Cup, run by the International Tennis Federation in November, bringing together 18 nations in one place for a week at the end of the 2019 season.
ATP Cup draw:
Group A (Brisbane) - Serbia, France, South Africa, Chile
Group B (Perth) - Spain, Japan, Georgia, Uruguay
Group C (Sydney) - Bulgaria, Belgium, Great Britain, Moldova
Group D (Perth) - Russia, Italy, USA, Norway
Group E (Sydney) - Austria, Croatia, Argentina, Poland
Group F (Brisbane) - Germany, Greece, Canada, Australia