Ahead of his 100th test for Australia in a Boxing Day match against South Africa in Melbourne, David Warner vowed to keep fighting despite having his back "up against the wall" after his recent struggles in cricket's longest format.

Warner has not scored a test century in almost three years, and his declining output has led to speculation he might retire from the format.

However, selectors have said he is part of Australia's plans for its tour of India starting in February.

Playing in his 100th test match "means the world to me," Warner told reporters. "It's the same old cliche but it's obviously a massive occasion.

"I'm living every housing commission boy's dream — I wanted to play cricket for Australia and I'm doing that now," said Warner, who was raised in public housing in an underprivileged neighbourhood of Matraville.

"My back's up against the wall but it's in my DNA to keep being competitive and take on whatever opposition I'm going to face ... I couldn't be any more proud of myself, my family for getting me here and my closest friends."

Warner struggled in the recent 2-0 whitewash of West Indies amid off-field distractions brought on by his aborted bid to have his permanent leadership ban lifted. He then scored 0 and 3 runs in Australia's victory over South Africa in the first test.

The 36-year old said his mental health was not where it "needed to be" ahead of the West Indies series, crediting his teammates and family for helping him through a difficult period.

"It's Christmas time, the festive part of year, I'm in a great headspace now getting ready for this training session and pumped to walk out and play another Boxing Day test, but more importantly with a series on the line," Warner said.