Novak Djokovic sparks US Open injury fears with concerning moment against Cameron Norrie

Cameron Norrie claimed Novak Djokovic has the tennis "level" to win a record 25th Grand Slam at the US Open. But the British No.2 questioned if the 38-year-old will have the physical staying power to get past Carlos Alcaraz and Jannik Sinner in the last four.

The four-time New York winner needed a medical timeout for treatment on his lower back in the first set. Yet the Serbian superstar recovered to win 6-4 6-7 6-2 6-3 to become the oldest man to reach the fourth round here since Jimmy Connors in 1991. He sent down 18 aces to equal his personal record in a US Open match. Norrie has still to beat a top-10 player in a Grand Slam - and has now lost all seven of his matches to Djokovic.

Asked if he has the level to win the title, the British No.2 said: "I think he has the level. Yes, the way he served today was, well, crazy. Especially at the beginning. But I think that the question lies physically. I mean, you can ask him just after me here, and see.

"But I think his tennis level, I was really impressed with it today. I was playing so well this tournament, feeling the ball well. He managed the match extremely well. Yeah, my level is a different level to Charlie and to Sinner, and to do that back to back is a different kind of challenge.

"I'm not sure, I think physically is the main thing. Depends on how he's feeling after this match. He stopped the match for the physio, he was calling the doctor. I'm not sure. You have to ask him."

Asked on court about his back injury, Djokovic said: "It is alright. I have had some ups and downs I guess. You don't want to reveal too much to rivals who are listening. I'm as young and as strong as ever. I'm still trying to find my groove. Today I played the best I have so far in the tournament."

Norrie agreed. Dressed in light blue and white, Norrie hit a purple patch when he took the second-set tiebreak when Djokovic served a double fault on the second set point. And the British No.2 produced two forehand winners - the second a superb drop shot - to break the Serbian superstar in the opening game of the third set. For a few minutes, mission impossible for Norrie seemed just possible.

But the 24-time Major champion won the next four games - helped by a Norrie double fault to get the first break - and order was restored. Dressed all in back for the night session, Swaggered around the Arthur Ashe Stadium like an old gunslinger

It was a familiar Djokovic story of injuries, delays and stunning shot-making.

"It was a really good match," said Norrie. "t was a tricky match. I think I've seen it before. I think you'll have to ask him with his back or his hamstring or his foot. I'm not sure what was going on.

It was a lot of stops and starts at the beginning, but he served incredibly well, maybe the best he's ever served against me.I was really impressed with him, and I told him I was impressed with his level when we shook hands. I had to play an insane game to break the serve, I think my only breakpoint I had, I took it."

Norrie also complained to German umpire Nico Helworth about the time Djokovic was taking between points. "I don't think it was a tactic, but I would have liked to see the umpire be a bit more assertive," said the former Wimbledon semi-finalist. "It changed nothing for the match.

"Yeah, just three or four times I had to wait for him on my serve. I was just asking the umpire what's the rule every time I have to wait for him. It was not a big deal, but I was just asking the question, because typically you play to the server's speed. He didn't tell him once anything. I didn't hear him. Maybe he did. No, it was not a factor in the match at all there."