Karen Khachanov gave up after getting injured at a crucial moment in his Paris Masters semi-final against Ugo Humbert.

The 2018 champion received treatment on his thigh during the final set. The issue continued to plague him, and he tripped up while serving to stay in the match, giving Humbert a match point.

Khachanov conceded defeat and let a ball fly past him to hand his opponent the win. And he had some confrontational words for the Frenchman as they shook hands at the net.

Khachanov was the favourite coming into his semi-final against Humbert. A former champion in Bercy, the Russian had also won the most matches during the European indoor swing so far this year.

He picked up the trophy in Almaty, reached the Vienna final and found himself back in the last four of the Paris Masters. The world No. 21 took a close first set in a tiebreak after 75 minutes but Humbert stormed back to force a decider.

And all of the tennis Khachanov has played recently finally caught up with him. He called the physio in the middle of the third set and received a medical time-out for an issue with his thigh.

Khachanov was clearly physically hampered when he resumed the match and was immediately broken and Humbert edged closer to his first Masters final.

Trouble struck when Khachanov served to stay in the match at 3-5. While 0-30 down, he tripped and fell to the ground when his leg gave way. "Well, he might not even finish this match," commentator Mikey Perera remarked.

Colin Fleming added: "I think it is completely gone there. That is horrible to see. Maybe just pushed the muscle over the edge."

The 2018 winner got back up and continued to play, now facing three match points. But he had already given up. As Humbert hit his second shot of the rally, Khachanov had already started walking to the net for the handshake and he let the ball fly past him to give the Frenchman the win.

They shook hands but the Russian clearly had something on his mind, turning back to confront Humbert. "Well there are some words between Karen Khachanov and Ugo Humbert," Perera said.

It appeared Khachanov wasn't best pleased with Humbert's celebrations while he was clearly struggling.

"Couple of words exchanged at the net. I think Khachanov - and maybe one or two people watching at home - maybe just feel like some of the celebrations were slightly too much," Fleming explained.

"Once he was a wounded warrior, the outcome felt inevitable. But of course Humbert, for me, it’s nothing against Khachanov, he’s just celebrating what is sort of a career moment so far.

"And the emotions just pouring out of him. You feel for Khachanov and of course he was right in that match. Brilliant end to the season, unfortunately his body just failing him in that third set."

Humbert will now face Alexander Zverev in Sunday's final. The world No. 18 is looking to become the first French Masters 1000 champion since Jo-Wilfried Tsonga in Canada more than a decade ago.

In the last year the Paris Masters will be staged in Bercy's Accor Arena before moving to La Defense, it would be fitting to see a home player crowned the champion.