In the 10 years that London has staged the season-ending ATP Finals - the event for the year's eight top players - Novak Djokovic and Roger Federer have been about as dominant as it's possible to imagine.
Nadal, who hopes to be ready for the tournament despite suffering from a right abdominal injury, has not won the event in eight attempts, although he has never competed in one when either of the other two have been missing.
The Spaniard said this week that he had had a scan in Mallorca after straining an abdominal muscle and would work on adapting his serve but he remained bullish about featuring at the ATP Finals after missing out past year with an injury.
Speaking after his Paris Masters win about his chances of claiming a record-equaling sixth year-end number one finish, Djokovic said: "There's always a chance that I win all my matches in London, that I play well".
'I have been serving very well in Bercy (Paris), I had good matches, so I am confident that I can be very competitive but of course it's a tournament that you will face the top guys since the beginning so you need to be 100 per cent ready.
"I need to see how things evolve every single day".
Final three hundred and sixty five days's champion, Zverev, 22, said upsets would change into extra frequent because the unusual era imposed themselves.
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"If I did I would be flying to China after NY because I was in a positive position".
"I think that's great that they're part of the finals. Not at all. I am fighting for it".
Dominic Thiem of Austria, at 26 slightly older than his young rivals, completes the field at the tournament featuring the year's best players, which starts on Sunday.
"Obviously, Rafa, Roger and Novak have been at the top for many years and they started from a young age", Zverev said. "I've historically played well in the indoor season".
"I have done it in the past, and I like playing there".
The clash between Djokovic and Federer is likely to be the highlight of the group stage, and it will be a first meeting since their dramatic Wimbledon final in July.
I hope he can get it together for 2020 because if I can pick a player that I think that can make it, then it would be Sascha.
Federer defended his decision to pull out of January's ATP Cup - where he had been due to face Andy Murray - for family reasons and revealed he will not play a tournament between here and the Australian Open, although he does have a number of exhibitions lined up.