Australian Open title hopeful Stefanos Tsitsipas is downplaying concerns over his fitness after sitting out part of Greece’s United Cup opening defeat to Chile.

World No.6 Tsitsipas was a late withdrawal from the men’s singles on Tuesday citing a back complaint.

The 25-year-old did make it out onto court to take part in the subsequent mixed doubles alongside world No.8 Maria Sakkari at Sydney’s Ken Rosewall Arena but wasn’t at his fluid best.

Tsitsipas and Sakkarri, who thrashed Daniela Seguel 6-0 6-1 in the women’s singles, fell 6-7 (7-5) 6-3 10-6 to Seguel and Tomas Barrios Vera in the mixed doubles.

Nicolas Jarry had earlier survived a scare at the hands of Tsitsipas’s replacement – towering 19-year-old Stefanos Sakellaridis – to claim a 6-3 3-6 7-5 victory before Chile went on to secure a 2-1 win across the tie.

And, while Sakellaridis’s performance against a player ranked close to 400 places above him was impressive, Tsitsipas’s fitness will be a huge concern ahead of the Australian Open.

The Greek, who was runner-up to Novak Djokovic in Melbourne last year, hadn’t played since withdrawing from an ATP Finals meeting with Holger Rune in Turin last November due to a back injury but he insisted he wasn’t overly concerned by his latest flare up.

“I’m much better than what I was a month ago,” Tsitsipas said.

“I wasn’t 100 per cent sure that I would have the chance to play the United Cup and it didn’t really cross my mind when I was considering my comeback.

“I went through tough times… Today, I was feeling great but there was just one moment during the match that I felt something.

“I don’t think I should be concerned about it too much, it’s not a major issue that I’m facing.”

Asked if had hopes of featuring in both the men’s singles and mixed doubles in Greece’s Group B tie with Canada on Wednesday, Tsitsipas said: “There’s a chance I might do both.”

Greece now need to beat the Canadians to have a chance of qualifying for the quarter-finals.

While the Greeks retain a glimmer of hope, Norway later topped Group F to advance without hitting a ball on Tuesday night.

The Netherlands’ mixed doubles win in a match tiebreaker in a 2-1 defeat to Croatia was enough for Norway to progress.

Source: AAP