Friday, top seed Novak Djokovic will play his U.S. Open semifinal against No. 10 seed Gael Monfils, and ticket holders would be forgiven for worrying that Monfils might get hurt.

So far in this year’s tournament, 10 players in the men’s draw either have retired during a match or, in one case, withdrawn with injury shortly before it was time to play. Three of those who quit — 30 percent — were matched against defending champion Djokovic.

Djokovic received a second-round walkover when Czech Jiri Vesely defaulted because of forearm inflammation, got a quick pass through the fourth round when Mikhail Youzhny’s hamstring injury sent him packing only six games into the match and he had a two-sets-to-none lead over Jo-Wilfried Tsonga in the quarterfinals when Tsonga was KO’d by a knee problem.

“I can only wish my opponents a speedy recovery,” Djokovic said. “That’s all I can do on my end. I’m sure it’s not an easy situation to handle.”

Unseeded Juan Martin del Potro, whose advance to the quarterfinals as a wild card is extremely rare, also benefitted from a retirement when his fourth-round opponent, Dominic Thiem, surrendered midway through the second set with a bad knee.

“It’s not good to win a match in this way,” del Potro said. “I’m very sad for him. I wish all the best. He’s a nice guy.”

In the women’s draw, there has been only a single in-match retirement through 120 matches. That was in the first round when Madison Brengle of Dover, Delaware, stopped playing in the sixth game of the second set against Kayla Day of Santa Barbara, California.

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Two women, Johanna Konta of Great Britain and Dominika Cibulkova of Slovakia demonstrated recuperative powers not seen on the men’s side. Konta fainted early in her second-round match against Tsvetana Pironkova of Bulgaria but revived herself and won that match, plus two more. Cibulkova appeared done in by a hamstring injury in the second round against Evgeniya Rodina of Russia, but bounced up to win that match and one more.

Djokovic, by the way, is not complaining about his lack of time on the court, needing only nine full sets to make it through five rounds. “One of the most important things for a player is this freshness of the mind, of the body,” he said. “I’m not going to practice for three or four hours just to feel that kind of potential for a fifth-set scenario.”