Novak Djokovic said he supported a domestic violence policy for tennis following allegations made against Alexander Zverev after the top seed reached the last four at the ATP Finals on Friday.
The Serbian beat his German opponent 6-3, 7-6 (7/4) and will play US Open champion Dominic Thiem in Saturday's semi-finals.
Zverev, who won the 2018 ATP Finals in London, has been competing under the shadow of serious abuse claims made by his ex-girlfriend Olga Sharypova.
He strongly denies the allegations, which were made by the former junior player on Instagram and in two media interviews, but has not addressed them in any detail.
The ATP, which runs the men's tour, had been criticised for not making any public comment until last week, when it issued a generic statement saying it "fully condemns any form of violence or abuse".
Several major American sports have a policy setting out a procedure to be followed in such situations, and Djokovic believes tennis should go down the same route.
"I've known Sascha (Zverev) for a very long time since he was very young," he said. "I always had a great relationship with him, he's a very nice guy. I have a lot of respect for him, his family. I was sad to hear that he's going through something like this.
"I don't know what happened. Obviously I'm not supporting any kind of violence. Whether ATP should develop a policy? Yes, why not? Probably it should be there in place."
Tennis has largely closed ranks around Zverev, with Australian Daria Gavrilova a notable exception in saying she believes Sharypova, and Djokovic has offered the German his support.
"He's been handling it well by the looks of his results in the last month-and-a-half or so. He's been doing well considering he's got a lot on his plate off the court," said the world number one.
"I sincerely wish for him that he overcomes this soon and that he can focus on his life and tennis career."
Zverev again implied he would not be taking legal action -- something Sharypova has also said -- and, despite the allegations and the coronavirus pandemic, declared it had been a "great year".
The 23-year-old reached the semi-finals at the Australian Open and the US Open final.