Cricket Australia defended underfire Usman Khawaja on Saturday for playing a round of golf on the eve of the first Ashes Test, where he failed to open the innings with back stiffness.

The 38-year-old left the Perth Stadium field on Friday near the end of England's innings where wickets were rapidly tumbling.

Because he was absent for more than eight minutes, he was not allowed to bat until the same amount of time had elapsed, as per the rules.

It meant Jake Weatherald was forced to front up with Marnus Labuschagne instead and the debutant opener was dismissed for a two-ball duck.

With the innings not yet eight minutes old, Steve Smith was then forced to come in at three, with Khawaja eventually showing at four. He survived just six balls.

Khawaja's failure to open, and initial uncertainty to why, sparked a wave of criticism from former greats with Tom Moody telling broadcaster ABC he was "stunned".

"Absolutely poor management," Moody said. "At the end of the day, to gamble on the fact that he could come back on the field when England is eight down (is a big risk).

"That is beyond a joke. He is our most experienced top-order player. We needed Khawaja at the front to lead the batting unit into this series."

Former Australia coach Darren Lehmann said it was "disappointing".

"We needed him out there facing the first ball," he added.

It later emerged that Khawaja skipped optional training on Thursday to play golf, but Cricket Australia chief Todd Greenberg said the back stiffness was a pre-existing issue.

"It's held him in good stead over the last couple of years," Greenberg told SEN radio of playing golf.

"It's not uncommon for a lot of them to play golf the day prior.

"A lot of people talk about cricket being played between the ears, and so getting some time away from being in your hotel or training I think is really important."

He pointed to Mitchell Starc being on the golf course with Khawaja, then taking 7-58 in England's first innings.

"I noticed Mitch Starc played golf with him, so it certainly didn't impact his performance," he said.

"Did that correlate to any of the issues? I personally don't think so.

"I think Usman's a very seasoned campaigner. He knows his body well and he knows how to get himself prepared for cricket, and he's done it over a long period of time. So I think that's drawing a long bow."