Novak Djokovic questioned a “stupid rule” after a contentious incident involving a video review during his China Open quarter-final against Alexander Zverev.

The controversy occurred after Zverev — who was serving at 1-0, 30-15 in the opening set — mishit a forehand out after Djokovic returned his big first serve.

After the point, Zverev made a complaint to chair umpire Adel Nour, who then announced that the German had requested a video review to check if a courtside LED advertising board changed during the point.

Replays confirmed that the display on a board at the side of the court changed during Zverev’s service motion, and the umpire ruled that this qualified as a let and decided the point should be replayed.

Djokovic expressed his confusion at this decision given that Zverev did not stop after his serve to make the request, and instead waited until he missed the forehand, which was unaffected by the board changing.

Speaking to the umpire, Djokovic said: “Okay, [the board changed when] he was about to serve… he served, I played one shot, he played another shot and then he challenged. Is that okay?

“If he was annoyed by that change there, he would stop after the serve and he would call it. It doesn’t make any sense.”

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Djokovic then said to Zverev, who had approached the net: “You missed the forehand, and then you challenged.”

Zverev replied: “Yeah, but I didn’t know if I could challenge or not, that’s why I came to him and asked him if I could challenge.”

In response, Djokovic said: “Yeah, but then you stop after the serve.”

Djokovic then continued his complaint to Nour.

“I mean, this must be one of the most stupid change of rules that I’ve heard in my life,” said the 24-time Grand Slam winner.

“There is no sense… if the player sees that there is a hinderance on that shot — he stops immediately.

“I mean, we can play a 30-shot rally, and he can lose the point, and he’s like, ‘Okay, I’m gonna challenge now’.”

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