Djokovic will lead Serbia at the second edition of the A$15 million event from December 29-January 7 before bidding for a record-extending 25th Grand Slam title at the Australian Open.
Team Poland, led by four-time major champion Iga Swiatek and 11th-ranked Hubert Hurkacz, are top seeds at the 16-nation tournament, which was won by the United States in January.
Nadal played for Spain in that edition and while he described it as a "great idea" he criticised the format for having teams play off in dead rubbers.
He was later beaten in the second round of his Australian Open title defence after aggravating a hip injury and has not returned to action since.
Tournament director Craig Tiley announced last week that Nadal would play in the next Australian Open in January but the Spaniard's representative said there was no date set for his comeback.
If fit, Nadal has a choice of other Australian Open warmup events in the leadup to the Grand Slam, including a pair of ATP tournaments in Adelaide from the 1st of January.
