Rafael Nadal and Novak Djokovic have disagreed on whether the best-of-five format at Grand Slams should be scrapped.
Both Nadal and Djokovic have enjoyed incredible success at Slams, winning 37 between them.
However, there has been a debate for several years whether the four majors should move to best-of-three set matches – like the rest of the ATP Tour - to help keep a younger audience engaged.
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The ATP Finals changed to a three-set final in 2008 while the Masters 1000 events also moved from best-of-five sets to three.
"I am completely against changing that in the Grand Slams,” said world No 2 Nadal after his win over Andrey Rublev at the ATP Finals.
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We have a day off. I think best-of-five makes a difference on these tournaments, on the Slams, and at the same time is part of the history of our sport, no?
Djokovic says he would be in favour of moving to best of three, citing the length of the tennis season and the need to attract younger fans as potential reasons.
"I am more a proponent of two-out-of-three everywhere, even though of course Slams have always been best of five.
"I don’t know whether there is a chance at all for it to change. I just feel that we have enough tournaments, enough matches during the year. We have the longest season of any sport in the world. Tennis has the longest season from January 1 to end of November.
"Unfortunately we had a stat that was a bit shocking - the average age of a tennis fan worldwide is 61. Obviously we have been one of those sports that has stuck with the tradition a lot, and I feel like this is something we have to keep, but we haven’t been really exploring, some changes, less sets, different calendar, different point system. We have not really looked into those."
World No 4 Daniil Medvedev agreed with Djokovic.
"If you ask me, I would change it to three sets. But I know that this opinion isn't very popular,” said the Russian after starting his ATP Finals bid with a win.