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.
The world number one offered his support to Zverev, who 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 also stated that she does not intend to press charges against the German.
"We don't know what happened truly. I mean, we are going to find out obviously," world number one Djokovic told reporters after his 6-3, 7-6(4) win over Zverev at the O2 Arena on Friday.
"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. So, we will have to wait and see."
Germany's Zverev has 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".
"In circumstances where allegations of violence or abuse are made against any member of the Tour, legal authorities investigate and due process, we then review the outcome and decide the appropriate course of action," the governing body of men's tennis said in a statement last week.
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. But I guess it wasn't developed and it wasn't there because we just did not have the cases like this," said Djokovic, who used to be president of the ATP's player council before he resigned earlier this year to form a breakaway association.
"I have not heard that we had maybe top players involved in such instances. So maybe that kind of case will in a way inspire ATP to do something like that."
World number seven 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."
