Lucas Herbert's major ambitions have suffered a setback after back pain forced the PGA Tour star to retire from the Australian PGA Championship midway through his second round.

A winner on the US and European tour, Herbert had hoped to use this week's event at Royal Queensland to boost his ranking up five places inside the top 50 to gain a spot at next year's Masters.

But, after taking anti-inflammatory tablets and battling through 10 holes on Friday, Herbert pulled the pin.

He said his physiotherapist's strong recommendation was to withdraw given the threat of a serious, long-term injury if he continued.

"I twinged my back this morning on the range, lost a lot of power in my swing," Herbert said.

"I tried everything I could to get going, I really wanted to keep playing and try and finish and make the cut and work my way up on the weekend.

"It's annoying because I don't think I've pulled out of a tournament mid-round. I'll do everything I can to get right for next week."

Herbert, who shot a one-over 72 on Thursday, still has time to force his way in to the top 50 by year's end to secure a ticket to the Masters, the opening major of 2023.

But the 26-year-old may need to win next week's Australian Open in Melbourne to do so.

Herbert boldly declared earlier this year that he could win the Masters on debut before missing the halfway cut at Augusta National.