Roger Federer added his heft to the growing debate around the controversial new-format Davis Cup, saying on Thursday that "this was not designed for me".
The inaugural Davis Cup finals are slated for a week in Madrid in November 2019 as part of a revamp to the competition, but it has been contentious with players.
Alexander Zverev, the world number five, said at the Shanghai Masters that he will not compete in the men's team event because it comes at the end of a long season.
Third-ranked Novak Djokovic agreed on Thursday that the timing was "really bad" and he also looks unlikely to feature.
And then Federer, the 20-time Grand Slam champion, added his voice to the debate when quizzed after beating Roberto Bautista Agut to reach the Shanghai quarter-finals.
"No, I highly doubt it, of course. We'll see what happens," said the 37-year-old, who has been carefully managing his schedule since 2017 to wring the most out of his ageing body.
"I don't think this was designed for me, anyhow.
"This was designed for the future generation of players."
Djokovic said that he is backing the rival ATP World Team Cup, set to take place weeks after the Davis Cup finals, at the start of the 2020 season.
The 31-year-old said there was "confusion" with the two competing events coming so close together and being so similar.
"I just feel like the date of the Davis Cup is really bad, especially for the top players," said Djokovic, echoing the strong sentiments of Zverev a day earlier.
"Between the two, I will prioritise the World Team Cup because that's a competition of ATP.
"But also I think and I hope that there will be a larger discussion between the players to understand how we are going to approach these two competitions.
"Or hopefully we can make it to the point where we can have one big 'Super World Cup', if you want to call it (that), or whatever it is, because that's the best thing for our sport.
"But the way it seems right now, we are going to have two at the moment."