Stefanos Tsitsipas pulled out of his top-10 showdown with Poland's Hubert Hurkacz at the ATP Cup Saturday with an elbow issue but then took to the court for a doubles clash, saying he was taking it "match-by-match".
The Greek world number four was due to face the world number nine in his season-opening game after compatriot Michail Pervolarakis lost 6-1, 6-4 to Poland's Kamil Majchrzak in the 16-nation event in Sydney.
But instead, Aristotelis Thanos played with Tsitsipas watching from the team bench.
The 23-year-old had right elbow surgery in late November after pulling out of the ATP Finals in Turin.
Thanos, ranked 1,076, stood no chance against a polished Hurkacz, who raced past him 6-1, 6-2 to seal the tie for Poland.
But Tsitsipas then appeared for the dead doubles rubber alongside Pervolarakis, showing no obvious signs of the problem as they won 6-4, 5-7, 10-8.
"The recovery from my elbow surgery in November is on track for Melbourne and today was a precautionary step to make sure I make Melbourne," said Tsitsipas, referring to the Australian Open that starts on January 17.
"We will see day-by-day, match-by-match until then."
He added: "I pray I am going to be able to play (singles) on Monday against Argentina."
In the other evening tie, Serbia's Filip Krajinovic beat Viktor Durasovic 6-2, 7-5 before Norway's world number eight Casper Ruud hit back by ousting Dusan Lajovic 6-3, 7-5. Serbia won the deciding doubles to take the tie.
Serbia won the inaugural edition of the ATP Cup in 2020, but that was with world number one Novak Djokovic.
He is not in Sydney after withdrawing last week, heightening doubts over whether he will defend his Australian Open title.
Djokovic has refused to confirm if he has been inoculated against Covid-19, a requirement at the opening Grand Slam of the year.
Earlier, Roberto Bautista Agut got Spain off to a perfect start with a crushing 6-0, 6-3 win over world number 17 Chilean Cristian Garin as he spearheads the team in Rafael Nadal's absence.
The 33-year-old, ranked two places below Garin, barely broke a sweat, ensuring Spain won their tie after teammate Pablo Carreno Busta came through 6-4, 7-6 (7/4) against Chile's Alejandro Tabilo.
"I played a very solid game, good rhythm, and good speed," said Bautista Agut. "I'm very happy because I won my point for the team."
Bautista Agut was part of the Nadal-led Spain team that made the final in 2020 when they were beaten by Serbia.
He is the lead singles player this time after 20-time Grand Slam champion Nadal opted to play an Australian Open lead-up event in Melbourne instead.
Whether Nadal would make it to Australia at all was in doubt after he tested positive for the coronavirus after an exhibition tournament in Abu Dhabi last month.
But he tweeted a photo of himself on an empty court at Melbourne Park late Friday with the comment: "Don't tell anyone... here I am."
A number of other players in Abu Dhabi also tested positive, including Russia's world number five Andrey Rublev, who is out of the ATP Cup.
Defending champions Russia, who beat Italy in last year's final, start their campaign on Sunday against France.
In other morning action, Argentina cruised past Georgia with world number 13 Diego Schwartzman annihilating 22nd-ranked Nikoloz Basilashvili 6-1, 6-2, and teammate Federico Delbonis thrashing Aleksandre Metreveli by the same score.
The winning nation from each of the four groups makes the semi-finals.
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