"Fernando's doctors have recommended to him that, following the concussion he sustained in a testing accident at the Circuit de Barcelona-Catalunya on February 22nd, for the time being he should seek to limit as far as is possible any environmental risk factors that could potentially result in his sustaining another concussion so soon after his previous one, so as to minimise the chances of second impact syndrome, as is normal medical procedure when treating athletes after concussions," McLaren said in a statement.
"Fernando has understood and accepted that advice, and the two McLaren-Honda cars will therefore be driven in Australia by Fernando's team-mate Jenson Button and the team's test and reserve driver Kevin Magnussen."
The 33-year-old Spaniard crashed into a wall at the track in Barcelona when he ran wide on the final day of the second pre-season test and had to be air-lifted to hospital under sedation.
McLaren chief executive Ron Dennis claimed last week that he couldn't "forsee any reason" why Alonso would miss the season opener in Melbourne.
Meanwhile, Alonso himself posted a video on social media saying he would be back racing "very soon."
However, McLaren remain hopeful that Alonso will be cleared to race in the second Grand Prix of the season in Malaysia on March 29.
"Indeed, his doctors are supportive of that ambition, satisfied as they are that he sustained no damage whatsoever during his testing accident on February 22nd.
"All at McLaren-Honda fully support Fernando's decision in respect of his doctors' advice.
