Top seed Novak Djokovic is concerned about his knee after he made it to the Paris Olympics semifinals by beating Stefanos Tsitsipas 6-3, 7-6(3) on Thursday night. Djokovic had to pull out of Roland Garros’ quarterfinal against Casper Ruud due to his knee injury.

The Serbian underwent surgery in Paris before Wimbledon and he was able to return to action in London. Djokovic also made it to the final at SW19 but could not cross the last hurdle against Carlos Alcaraz as suffered a straight-set loss.

The Serb admitted he felt sharp pain in the second set against Tsitsipas on Thursday.

“I’m concerned about the state of the knee. I cannot give you exact information, because I don’t have it. I have to go and examine the knee now with my physio and with the medical staff of the tournament. And then let’s see,” said Djokovic, a 37-year-old from Serbia who will face Lorenzo Musetti of Italy on Friday.

“I’m hoping,” Djokovic said, “I can be ready.”

Djokovic added he would have a clear picture on his fitness on Friday morning.

The medicine helped matters, Djokovic said, “But that effect is going to fade away tomorrow morning. So I will have probably a more realistic picture tomorrow and hope for the best.”

On the other hand, Tsitsipas had the opportunity to take the match into third set as he was serving at 5-3, 40-0 but could not convert three set points.

“I feel like I could have done so much more today,” Tsitsipas said. “Novak is one of the best players in the world. He … did give me a lesson: I should be much more into the match whenever I have the opportunity to close it, and today I didn’t show that.”

Meanwhile, Carlos Alcaraz will face Canada’s Felix Auger-Aliassime in the other semifinal.