World number two Rafael Nadal on Tuesday pulled out of Spain’s opening ATP Cup tie against Australia due to a stiff lower back, reported AFP.

Nadal was set to play against Australia’s top-ranked player Alex De Minaur, but decided to take a rest instead as he prepares for the Australian Open next week.

The 20-time Grand Slam champion said in a tweet, “Hi all, we have decided with Team Spain and my team, to not play today the first match of the ATP Cup here in Melbourne since I have a stiff low back.”

“Hopefully, I’ll be better for Thursday,” he added.

While Spanish number two Roberto Bautista Agut will take on De Minaur, John Millman will face Pablo Carreno Busta in the opening rubber.

Nadal is aiming for a record-breaking 21st Slam title in Melbourne, moving him past the injured Roger Federer. He played an exhibition in Adelaide on Friday, beating Dominic Thiem 7-5, 6-4.

Australian Open organisers said on Saturday that daily spectators of between 25,000 and 30,000 will be allowed in the park. 

Victoria state’s Sports Minister Martin Pakula said, “It will not be the same as the last few years, but it will be the most significant international event with crowds that the world has seen for many, many months.”