Nadal out of season-opening Abu Dhabi event

'It was a tough 2017 and I need to take my calendar in a different way in order to be ready.'

Rafael Nadal has withdrawn from next week's season-opening exhibition event in Abu Dhabi due to ongoing fitness problems, the world number one said.

The 16-time Grand Slam champion, who won the French and US Opens earlier this year, withdrew from the ATP Finals in November after struggling with a knee injury during his round-robin defeat by Belgian David Goffin.

The 31-year-old Spaniard, who has previously played at the tournament on eight occasions, will be replaced by compatriot Roberto Bautista Agut.

"It was a tough 2017 and I need to take my calendar in a different way in order to be ready," Nadal told the Mubadala World Tennis Championships website.

"For this reason, I have sadly announced to the organisers and now to you fans that I won't play this time in Abu Dhabi."

Stan Wawrinka and Milos Raonic have also withdrawn from the tournament, which is held from Dec. 28-30.

The Australian Open, the first major of the new season, begins on January 15.