"I hope we can come back before the end of the year but unfortunately I don't think so," Spanish newspaper El Pais told the world number two on Tuesday.
The pandemic has led to Wimbledon being cancelled and the French Open being postponed to September, while the U.S. status has been postponed. Open, scheduled to be held late August as usual, is still unclear.
Nevertheless, Nadal said he had almost written off the rest of the year and looked to the Australian Open in January 2021 as the next tournament he'll play.
"I'd sign up to be ready by 2021," added the Spaniard.
"I worry about the Australian Open more than what happens at the end of this year. I believe 2020 is virtually lost. I hope that next year we can start again, I really hope that's the case.'