The ATP – as it stands – is a 10-month long season starting in January and finishing with the World Tour Finals in November.
Last month, Zverev was very vocal in voicing his displeasure about how the players have been affected and are generally feeling more tired as the campaign wears on.
Federer wasn’t left entirely convinced by Zverev’s argument while Djokovic has also moaned about the busy calendar.
And Philippoussis – who reached two Grand Slam finals in his career – has sided with Federer.
“I think it [the schedule] is done well,” he told Metro.
“The only difference is we’re the only sport in the world with no off-season. That’s the difference.
“But Federer said it perfectly, right? It’s different for someone like Federer or guys who are comfortable, getting paid well that can take weeks off.
“At the end of the day we have a job where you can walk away for a month, a week, two weeks, six months.
“You’ve got sponsors but if mentally you need to get away for a month, you can do that.”
Philippoussis also believes the players can pick and choose what tournaments they want.
“What other job can you do that, right? Tennis players are incredibly fortunate to be in that position,” he added.
“They don’t have an off-season but at the same time you don’t have to play 34 tournaments a year, you can play 16.
“Guys who are complaining about playing too much are the same guys playing 30-something tournaments a year.
“You don’t have to play, they’re the ones who are electing to do it.
“After the Grand Slam and the Masters events where they don’t get paid appearance fees, the times where you normally get time off is when these other tournaments are offering you 200 grand, 300 grand to play – and that’s why these guys aren’t saying no.
“They’re saying yes, they’re playing.”