A frustrated David Nalbandian [ Images ] is fighting to be fit for next week's Australian Open [ Images ] after pulling out of the warm-up event at Kooyong because of a back injury.

The Argentine, who ended last year by winning back-to-back Masters Series titles in Madrid and Paris, suffered back spasms during a practice session at Melbourne [ Images ] Park on Wednesday.

Nalbandian will have an MRI scan on the injury later in the day but has been told to rest for at least three days, leaving him just a couple of days to prepare for the first grand-slam event of the year.

"I think I am going to be OK, but you never know," Nalbandian told reporters.

"I had what they say is a distension in the back. I have four, five days to go. I will try to hit on Saturday for 30-40 minutes and see how it is."

Nalbandian was considered one of the favourites for the title at Melbourne Park, having ended the season on a high with his back-to-back Masters Series wins.

The world number nine was practising with former number one Marat Safin [ Images ] of Russia [ Images ] when he first felt pain.

"I started to feel some pain after about 30 minutes. I tried to keep going all the way with Marat -- we were playing points -- but I couldn't continue."

Nalbandian said he had arrived in Melbourne feeling fully fit and ready to bid for his first grand-slam title.

"I felt perfect," he said.

"I was just resting for two weeks, so for a month and a half, I have been practising. I feel great, fit and everything, so it was just bad luck today."

Nalbandian's place in the eight-man Kooyong field will be taken by Brydan Klein, who won the boys' title at the Australian Open last year.