A frustrated David Nalbandian is fighting to be fit for next week's Australian Open 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 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.

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