Monte Carlo (Principality of Monaco) (AFP) - World number one Rafael Nadal said on Sunday that the introduction of a shot clock could cause problems, especially after particularly gruelling points.
A 25-second shot clock is set to be used at the US Open later this year, in order to stronger enforce rules on how long a player can take between points on serve.
Nadal is one of the slowest top-ranked players, and was docked a first serve for taking too much time during a match en route to his 10th French Open triumph last year.
"For me it's not the ideal thing but if the sport is moving that way or they want to move that way, the only thing I can do is accept it and play," said the Spaniard ahead of his Monte Carlo Masters title defence.
"That's why I am here, to play tennis and to accept all the rules.
"The positive thing is probably you will control the time between points but in the negative thing... In my experience, on the tennis court, the crowd gets more crazy, the crowd gets more emotional and enjoys the match with more passion when you play good points."
Nadal argued that it would be tougher for players to recover between lengthy rallies if restricted to just 25 seconds, especially in front of a vocal crowd.
"It's obvious that sometimes when you play a rally with 56 shots as I did with Novak (Djokovic) a couple of years ago in the final (US Open 2013), you cannot expect a good point if you have 25 seconds on the next point," said the 16-time Grand Slam champion.
"Maybe for the business it's better but in my opinion for the good show and the show that the people get more involved, it's probably more a negative thing."
The shot clock was trialled during US Open qualifying last year, and was also used at the 2017 NextGen Finals in Milan and the exhibition International Premier Tennis League.
"I played only with the shot clock in IPTL and it was only 20 seconds. In some cases it was working well and some cases not," said world number three Marin Cilic.
"Some ball boys were ready for that, some were better, some were not. I think it needs to be slightly balanced but I think it can be good for tennis to have something like that."
Rising German star Alexander Zverev also brushed off any concerns, pointing out that he is one of the quickest players on tour alongside Australian Nick Kyrgios.