Felix Auger-Aliassime leaves commentators baffled after retiring suddenly at Swiss Indoors

Felix Auger-Aliassime stunned commentators when he suddenly retired after losing the first set of his quarter-final match at the Swiss Indoors. The Canadian star was on a six-match winning streak after lifting the title at the Brussels Open over the weekend and showed no real signs of discomfort before calling it quits when Jaume Munar took the first set 6-3.

Auger-Aliassime is still in contention to qualify for the ATP Finals. But his mid-match retirement hasn't helped his chances - Auger-Aliassime now remains at No. 9 in the race, with the eight players who have earned the most ranking points this season making the cut. And some of his rivals will now be able to overtake him if they have deep runs at this week's ATP 500 events in Basel and Vienna.

Munar played a statement first set, dropping just one point on serve and recording an overall performance rating of 9.1. He served it out to love in 44 minutes and then headed to his bench for the changeover when Auger-Aliassime called it quits.

The Spanish star seemed surprised as the No. 5 seed approached his bench to shake hands, before packing his belongings and leaving the court, waving goodbye to the crowd.

"Oh, where on earth has that come from? Auger-Aliassime has retired," Adam Fielder said on commentary.

"Well we saw him, very early in the match, kind of stretching out his back but there were no concerns thereafter, and I think that has caught everyone off guard. Let's hope that that is just a precautionary measure and he's going to be okay to lace them up in Paris next week."

Co-commentator Jonathan Overend replied: "I mean, startling in terms of the sudden-ness of the decision there from Felix. As you say, there was that one off forehand he hit early on in the match and he was grimacing and holding his lower back after playing it.

"It was an awkward one, he had to change direction of his hips to play it. Hopefully, as you say, it's just precautionary, because with Paris still to come, more ranking points available there, there is still a big chance - maybe he's just taken a calculated decision - that it's better to be fit for Paris than it is risking further injury here."

Auger-Aliassime's retirement officially went down as a lower back injury. The world No. 12 now has just a few days to recover in time for next week's Paris Masters, where up to 1,000 ranking points are up for grabs as he makes a last-gasp attempt to qualify for the ATP Finals.

The Canadian could now be overtaken in the 'Race to Turin' if Casper Ruud wins the title in Basel this week. Ruud would jump ahead to ninth in the race, and Auger-Aliassime would drop to 10th.

The 25-year-old was a two-time former champion in Basel. He beat Marin Cilic and Gabriel Diallo on his way to this week's quarter-final before his shock retirement.

Munar is now through to his second career ATP 500 semi-final, where he takes on the winner of a clash between Denis Shapovalov and Joao Fonseca.

Meanwhile, over at the other ATP 500 tournament in Vienna, there has been another withdrawal. Dutchman Tallon Griekspoor pulled out of the event moments before he was due to take to the court to face second seed Alexander Zverev.

It means Zverev has qualified for the ATP Finals, joining Carlos Alcaraz, Jannik Sinner, and Novak Djokovic.