Novak Djokovic received treatment for a wrist issue during his 6-1 6-7 (3) 6-1 win over Jiri Lehecka at the United Cup Tuesday as Serbia squeezed past the Czech Republic 2-1 to reach the quarter-finals.
Djokovic drew Serbia level at 1-1 in the $10m mixed team tournament and had been scheduled to compete in the mixed doubles decider with Olga Danilovic before being replaced by the 20-year old Hamad Medjedovic.
The young Serbian duo overcame Petr Nouza and Miriam Kolodziejova 4-6 7-6 (2) 10-8 to send Serbia into the last eight where they will play hosts Australia Wednesday.
Djokovic, gearing up for a tilt at a record-extending 11th Australian Open title this month, appeared to be bothered by his right wrist in practice and occasionally grimaced in the opening set at RAC Arena.
The Serb had his wrist worked on by a trainer after the first set and Lehecka sensed an opportunity, winning the second set in a tiebreak.
Djokovic took a medical timeout before the start of the third and came out firing, running up a 5-0 lead before sealing the match.
"(The injury) happened in the warm-up before the match. I basically got constant treatment before the match, during the match, after the match," the 36-year old told reporters.
"It's not the first time that I have faced these kind of circumstances...these things happen. I think it's not a major concern, because I still managed to finish the match and managed to play well, even though I maybe wasn't feeling 100%.
"Hopefully I'll have enough time to recover for the tie against Australia."
Wimbledon champion Marketa Vondrousova had earlier given the Czechs a 1-0 lead by beating Danilovic 6-1 3-6 6-3.
Poland will take on China in Wednesday's other quarter-final in Perth.
Greece were stunned by Chile in their Group B opener, with Maria Sakkari and Stefanos Tsitsipas losing 6-7 (5) 6-3 10-6 to Daniela Seguel and Tomas Barrios Vera in the mixed doubles decider in Sydney's Ken Rosewall Arena.
Sakkari beat Seguel 6-0 6-1 in the opener before Chile's Jarry downed Stefanos Sakellaridis 6-3 3-6 7-5 to level the tie after the Greeks decided not to field Australian Open runner-up Tsitsipas in the singles.
Croatia beat the Netherlands 2-1 in their United Cup Group F tie but Norway edged them to top the group with a better games winning percentage and advance to the quarter-finals.
Croatia needed a 3-0 result or a 2-1 win with a 5-2 sets score to finish at the top.
But after Borna Coric and Donna Vekic won their singles rubbers, the mixed doubles match was clinched by the Dutch duo of Demi Schuurs and Wesley Koolhof.
"It was very close, it could have gone both ways. But of course, we wanted to win in two sets and we knew that before the match," Schuurs said.
Croatia can still advance as one of the best second-placed teams.
The Australian Open runs from January 14-28 at Melbourne Park.