Novak Djokovic said tennis authorities could adopt clearer policies on domestic abuse in light of allegations made against US Open runner-up Alexander Zverev by his ex-girlfriend.

Zverev has repeatedly denied the allegations made by Olga Sharypova.

In an interview with Racquet Magazine, Sharypova said Zverev was emotionally and physically abusive to her. She stated that she does not intend to press charges against the German.

Djokovic responded to questios from reporters after his win over Zverev at the ATP Finals in London on Friday.

“We don’t know what happened truly. I mean, we are going to find out obviously,” he said.

“I have known Sascha for a very long time since he was very young. I always had a great relationship with him. Very nice guy. I have a lot of respect for him, his family.

“So I was sad to hear and to know he’s going through something like this.

“I don’t know what happened. Of course, I mean, obviously I’m not supporting any kind of violence.”

Germany’s Zverev described the allegations as “unfounded and untrue” and without any legal investigation the men’s ATP Tour would be unlikely to intervene.

The ATP said it condemned “any form of violence or abuse”.

World No.1 Djokovic was asked whether the ATP should adopt its own policy on domestic abuse, similar to those in American sports, regardless of legal proceedings.

“Yeah, I mean, why not? Probably it should be there in place,” he said.

“But I guess it wasn’t developed and it wasn’t there because we just did not have the cases like this… So maybe that kind of case will in a way inspire ATP to do something like that.”

Djokovic was president of the ATP’s player council before he resigned earlier this year to form a breakaway association.

He has since been nominated for a return to the player council.

World No.7 Zverev said he had nothing to hide.

“The players know what’s going on,” the 23-year-old told reporters after he was beaten by Djokovic in his final round robin match on Friday.

“What else can I say? I have said everything that I can.

“It’s very unfortunate that these kind of false allegations can put such damage and put the attention away from the sport, but it’s the world we live in right now unfortunately.

“There is nothing more that I can do.”