The Spaniard, the top seed in the tournament, was set to face Jo-Wilfried Tsonga in a blockbuster second-round match before deciding to take precautionary measures leading up to the season's first major in Melbourne.
Nadal explains decision to withdraw
In a press conference to announce his decision, the 17-time major champion said "I did an MRI and it shows a small staring on my left thigh. I wanted to play, but all the recommendations from the doctors were if I play, there is a risk, an important risk to don't have the chance to play Melbourne. I can't do my 100 percent".
The Spaniard was scheduled to play in his first ATP World Tour event since retiring in last year's U.S. Open semifinals. Nadal played in an exhibition in Mubadala last week, losing to Kevin Anderson before withdrawing.
"It's a small thing that could become much bigger", Nadal would go on to say. "When you compete the intensity on the muscle, it can get worse. I feel better than I did four days ago.....it's a risk to damage my body for one month if I play here".
Speaking about his chances at the Australian Open, the 2009 champion stated "my hope is to win the Australian Open and being honest, I feel myself playing well. I feel myself playing at a good level of tennis. I really believe that I will be 100 percent ready for Melbourne".
Japan's Taro Daniel will take Nadal's spot in the draw in Brisbane as a lucky loser.