But the world No 1 still hopes to play the Australian Open next month and build on his stunning year.
Nadal finished his 2017 in disappointment when he withdrew from the ATP finals in London after one match – a defeat to David Goffin – but won two Grand Slams to move back to top of the rankings.
However his start to the 2018 is now uncertain.
He will definitely miss the first event he was scheduled for but will head to Australia at the turn of the year and hopes to play in the first slam.
“I am still not ready after last year’s long season and the late start of my preparation,” said Spaniard Nadal, 31.
“I’ve got to try and keep it cool. Try my best and see what happens but the preparation has been good so far,” he added.
“We’ll see how things go.”
He did however claim he wants to play in Melbourne.
“I will be seeing my Aussie fans when I land on the fourth in Melbourne and start there my preparation for the Australian Open,” he said.
British number one Andy Murray is due to play in the tournament as he embarks on his comeback from a hip injury.
Sky Sports tennis expert Annabel Croft has admitted she’s unsure if Nadal will be able to maintain his form from last year due to his knee issues.
“There’s always rumours about Rafa’s knee,” she told Express Sport.
“I’ve ready a lot of reports about him cancelling a training camp, so I think a lot with him will depend on the knee, but Federer definitely.
“I think he’s playing the best tennis we’ve ever ever seen him play.”