Novak Djokovic, who famously said winning the Davis Cup with Serbia in 2010 changed his career, gave voice day to the widely held but rarely spoken fear that the largest annual international team competition in sport – and one of the oldest – is fighting for its life.

On the eve of the ATP launch here of their own World Team Cup in January 2020, Djokovic, the president of the association’s players’ council, said tennis will have to choose sooner rather than later between the new competition and the 118-year-old Davis Cup, which is being re-booted as a round-robin event next November.

France host Croatia in the last final under the old format in Lille next week, but the competition has the smell of insurrection about it. The rising star of the game, Alexander Zverev, doubts many of the leading players will bother playing in it.

Speaking after a routine 6-4, 6-1 win over Zverev launched him into the semi-finals of the ATP World Tour Finals for the eighth time, Djokovic said: “We have to deal with it right now. In the next two years we’ll have both events happening in a very similar format if not the same, six weeks apart. I honestly don’t think it’s good for the sport.

“[It creates] more job opportunities for players, yes. But it’s not sustainable. We will have two average events. Creating one event is an ideal outcome for everyone. From what I’ve heard from conversations with people from different sides in this sport, they all want to have one event, because it’s over-saturated. We have the longest season in all sports. We’re just adding events. We have to focus on quality rather than quantity.”

Djokovic, who returned to No 1 in the world this month to cap a remarkable comeback (he lost three matches in a row in the first weeks of his 2018 return) added: “I don’t necessarily think money is the driving factor. It might appear so. In certain situations, obviously yes [The Rod Laver Cup exhibition tournament in Chicago this year offered the best players $750,000 for a week’s tennis]. But, as president of the [players’] council, I’ve had the opportunity to meet with the most powerful people in our sport in the last couple of years. The majority [of them] really care about this sport deeply.

“There are many interested sides. It is not as simple as just let’s pull the trigger and make this happen or this radical move within a month. It doesn’t work that way. There are members, constituents, boards. Everything has to be voted. I think the structure of the ATP, specifically, can be better. I don’t think it’s working very well, to be honest. It’s a slow process. The Davis Cup and World Team Cup situation is delicate.”

He added: “The Laver Cup is not an official competition. It doesn’t have [ranking] points. But it has to be regarded as a very successful, very serious competition. I was part of it this year. I can definitely say it has attracted a lot of success and attention. So far it’s been the only competition that can actually get the biggest rivals in sport in one team. That was a unique experience.

“This part of the year, after the grand slam season is done, you have post-US Open, Laver Cup, then Davis Cup, World Team Cup first week of the year. It’s over-saturated. Within three, four months, it’s too many events. We’ll have to work it out. But we have to start from somewhere.”

On the court, the 31-year-old five-time champion still had way too much zip for 21-year-old Zverev, who saved two break points in the 10th game before gifting the favourite an otherwise tight first set after 47 minutes with a double fault. It was a triumph of patience and experience over aggression.

The young German’s unforced error count grew as he over-reached in an effort to get back on level terms. When he pushed a tired backhand wide from the baseline to hand Djokovic the break in the fourth game, the fight was all but done. Down a set and 1-4 after an hour and 10 minutes, Zverev continued to go for big winners from even half chances, but a second double fault handed Djokovic three break points in the sixth game. He wrapped it up after a deep forehand drew a weary, over-cooked response from his disheartened opponent. The title is now his to lose, but there are other battles looming.

Djokovic’s passage was sealed when Marin Cilic outlasted John Isner over two-and-a-quarter hours in the evening session to win 6-7 (2), 6-3, 6-4. “It was extremely tough,” Cilic said. “I served really well in the third set. It was a tough one in Paris [when he lost to Djokovic]. Novak is playing really good tennis.”