The world No.1 was troubled by his right wrist during practice on Tuesday morning, with the injury requiring intense treatment from his physio.
Djokovic was cleared to play his singles match against Jiri Lehecka later in the day and it was just as well given Wimbledon champion Marketa Vondrousova defeated Olga Danilovic 6-1 3-6 6-3 to give the Czech Republic a 1-0 lead in the tie.
Novak Djokovic proved too strong for Jiri Lehecka of the Czech Republic winning 6-1 6-7 (7-3) 6-1. (Richard Wainwright/AAP PHOTOS)
The 24-time grand slam winner looked on track for an easy victory against Lehecka after winning the first set and shooting out to a 3-1 lead in the second.
But with his wrist troubles growing as the match wore on, Djokovic started making a series of uncharacteristic unforced errors.
He took a medical time-out after losing the second-set tiebreak and came out firing with a double break in the third set to seal the 6-1 6-7 (7-3) 6-1 victory.
Djokovic is confident the wrist injury won't hold him back for his highly anticipated match-up against world No.12 Alex de Minaur in Perth on Wednesday night.
"I think it's not a major concern because I still managed to finish the match. I managed to play well," Djokovic said."Even though I maybe wasn't feeling 100 per cent, it still allowed me to finish the match.Â
"So hopefully I'll have enough time to recover for tomorrow's tie against Australia that is in the afternoon hours, so more time for us."
Confusion reigned after Djokovic's singles win on Tuesday as to whether Serbia had already done enough to qualify for the quarter-finals.
The initial declaration from officials was even if Serbia went on to lose the mixed doubles and therefore the tie, they would qualify for the quarter-finals as the best second-placed team in Perth.
But that proved to be wrong with organisers later clarifying Serbia would be out if they lost the mixed doubles in straight sets.
Djokovic opted out of the mixed doubles to rest his wrist and he faced a nervous wait to see if his teammates could pull through.
Things looked bleak for Serbia after Danilovic and Hamad Medjedovic lost the first set to Miriam Kolodziejova and Petr Nouza.
But Serbia's passage was safe when they won the second set in a tiebreak, with Djokovic clearly delighted and relieved as he watched on from the sidelines.
Serbia went on to win the clash 4-6 7-6 (7-2) 10-8 in a match tiebreak.
The Team Serbia show rolls on 🇷🇸— United Cup (@UnitedCupTennis) #UnitedCup pic.twitter.com/amdl8sSK0TJanuary 2, 2024
"It was quite tight for them on the court, but also us sitting and watching," Djokovic said.
"Everybody was very, very nervous knowing that we needed a set.
"I'm proud of them for raising the level and making it happen for Serbia. We are through. That's all that matters."
Serbia topped Group E with the tie win and they will take on Group C winners Australia at Perth's RAC Arena in front of a bumper crowd.
That will pit Djokovic up against de Minaur, who showcased his potential with a devastating 6-4 6-2 win over world No.10 Taylor Fritz on Monday.
Poland will face China in the other quarter-final in Perth.
Djokovic destroyed de Minaur 6-2 6-1 6-2 in the fourth round of last summer's Australian Open in the only head-to-head battle between the pair to date.
