Madrid - World number two Rafa Nadal yesterday 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 practised for an hour yesterday at the Rod Laver Arena and his fitness was improving "little by little, step by step", sources close to Nadal said.

The Spaniard was one of the top players who quarantined in Adelaide for 14 days after their arrival Down Under and were allowed five hours a day to train during the mandatory isolation.

He then defeated Dominic Thiem 7-5 6-4 on Friday in an exhibition match between the men's world number two and three at Adelaide's Memorial Drive Tennis Club.

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. - Reuters