Tennis world in shock over Alexander Zverev incident at French Open

The French Open was rocked by sickening scenes on Friday when Alexander Zverev was forced to retire hurt in his semi-final clash with Rafa Nadal when he injured his ankle.

Nadal reached the 14th Roland Garros final of his storied career after Zverev went down in agony after twisting his ankle while trying to retrieve a ball.

SO GOOD: Coco Gauff in never-before-seen feat at French Open

SAY WHAT: Rafa Nadal backflips after retirement speculation

In distressing scenes at Roland Garros, the German third seed fell and twisted his right ankle towards the end of the second set, screaming out in pain as Nadal rushed around the net to help.

Zverev was helped to his feet and taken off the court in a wheelchair for treatment.

After five minutes the 25-year-old re-emerged on crutches to inform the umpire and Nadal that he could not continue.

The crowd on Philippe-Chatrier - fiercely pro-Nadal as usual - rose to salute the World No.3 as his latest bid for a grand slam title came to a devastating end.

"It's very tough, very sad for him," Nadal said in his on-court interview.

"He was playing an unbelievable tournament, and I know he was fighting to win a grand slam.

"I'm sure he will win more than one and I wish him all the best."

Nadal had won the first set in a tiebreaker and the second was evenly poised at 6-6 when disaster struck for Zverev.

Speaking on Eurosport Germany, Zverev's brother Mischa said: "Sascha never cries. Something bad must have happened. That's impossible!

"The ankle was gone. That was an angle, in that position nothing can stick. He couldn't get up. He was really screaming."

Tennis fans and commentators were left shocked by the awful moment.

Rafa Nadal and Casper Ruud in French Open final

On his 36th birthday, Nadal was broken in the very first game of the match and was behind the eight ball for most of the opening set.

He was standing as far back in the court as possible as he defended Zverev's thunderous serve. Had the wall not been there to stop him, Nadal would probably have stood in the crepe stand outside.

Having clawed the break back he found himself facing four set points at 6-2 down in the tie-break but somehow hit back, including one improbable backhand get followed by an outrageous forehand winner, snatching it 10-8 after 92 gruelling minutes.

“Only thing that I can say is I hope he’s not too bad. Hopefully it’s just the normal thing when you turn your ankle, and hopefully nothing (is broken). That’s what everybody hopes,” Nadal said.

“Even if for me it’s a dream to be in the final of Roland Garros, of course that way is not the way that we want it to be. ... If you are human, you should feel very sorry for a colleague.”

Meanwhile, Casper Ruud became the first man from Norway to reach a grand slam final, eliminating 2014 US Open champion Marin Cilic 3-6, 6-4, 6-2, 6-2 in a match interrupted for more than 10 minutes in the third set by a climate activist who attached herself to the net and knelt on the court.

The 23-year-old Ruud has never faced Nadal but trained at the King of Clay's academy in Mallorca.

“He's a perfect example of how you should behave on court: Never give up and never complain. He’s been my idol for all my life,” said Ruud.

“I guess this is perfect timing and worth the wait to finally play him in a grand slam final.”

with agencies

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.