Alexander Zverev in agony at the French Open. | Yves Herman

Rafael Nadal's quest for a 14th French Open titles continues, but on Friday at Roland Garros it was at the expense of an injured Alexander Zverev, who was forced to retire before the end of the second set.

Third seed Zverev, in a great deal of pain after a fall, reappeared on court on crutches to hear Nadal say: "It was very tough and very sad for him. He was playing an unbelievable tournament. He's a very good colleague on the tour, I know how much he is fighting to win a Grand Slam.

"For the moment, he was very unlucky. The only thing I am sure is that he is not going to win just one but more than one. I wish him all the best and a very fast recovery."

Nadal added that it had been a "super tough" match, and it had been. The first set lasted 91 minutes, Nadal eventually winning the tie break 10-8. When the match finished, it was six-all in the second.

In the final, Nadal, who was celebrating his 36th birthday on Friday, will play either Casper Ruud or Marin Cilic.