Goran Ivanisevic insisted Sunday there is "no debate" that Novak Djokovic is the greatest player of all time.
Djokovic won a record-equalling 20th Grand Slam title and sixth Wimbledon on Sunday with a 6-7 (4/7), 6-4, 6-4, 6-3 victory over Italy's Matteo Berrettini.
The world number one has now moved level on 20 majors with Roger Federer and Rafael Nadal.
If he wins a fourth US Open in September, he will become the first man since Rod Laver in 1969 to complete the calendar Grand Slam and just the third in history.
"For me Novak is the best ever. He's writing history. He's going to do it in US Open. I strongly believe he's going to do it, he's going to win all four in one year. Then I think story's over," said Ivanisevic, one of the world number one's coaches and a former Wimbledon champion.
"For me it was over a long time ago. It's just who you like more. Between these three guys, 60 Grand Slams.
"It's unreal. For me, not because I'm here, before I was a member of the team, for me he was the best.
"I say he's the only guy who can win four in a row in the same year.
"If he wins US Open, I think it's over. He wants to win more. But for me Novak is the biggest ever. I don't even have to debate about that."