MADRID: World number two Rafa Nadal on Thursday said doubts remain over his fitness ahead of next week's Australian Open.

Nadal pulled out of Spain's ATP Cup tie against Australia on Tuesday with a lower back problem and, despite some improvement, said he was still far away from the level required to play at the year's first Grand Slam.

"It's not that I'm in a really bad way, but I'm also not alright in the sense that I can't play either," Nadal told Spanish television channel Movistar+.

"I've improved a little but I'm not in a position where I can go and play a game at full intensity."

Nadal's name was also absent from Spain's ATP Cup tie on Friday against Greece at Melbourne Park's John Cain Arena with Roberto Bautista Agut and Pablo Carreno Busta to lead the challenge in the singles matches for last year's finalists.

The 34-year-old, however, practised for an hour on Thursday evening at the Rod Laver Arena and his fitness was improving "little by little, step by step", a source close to Nadal told Reuters.

Nadal sits level with Roger Federer on 20 Grand Slam titles and, with the Swiss not taking part in Melbourne after knee surgery, the Spaniard would have the chance to become the all-time major record holder in the men's game for the first time.

He insisted, however, that that was not something he was focused on. "First thing's first, and that's to play the Australian Open, and if that doesn't go well, the season goes on," he said.

"I've never been obsessed with Grand Slams, truth be told."