The tighthead prop was due to rejoin the Brumbies ahead of their round one clash against the Reds at GIO Stadium, but will instead undergo surgery on his injury.
Brumbies coach Dan McKellar said the club would look at replacement options but it may mean a call-up to action for 2019 Junior Wallabies prop Bo Abra, who has been training with the team in Leulua’iali’i-Makin’s absence.
"Firstly we're devastated for Les. He's represented the jersey 50 times and is such a big part of the organisation and well loved by the playing group and staff,” McKellar said.
"As a club, we will be doing all we can to help support him through his surgery and our medical staff will be there to help him with his rehab in order to get him back on the field as soon as possible.
"We'll be having a look around to see who's available as a replacement but we are happy with how Bo Abra is progressing after training with our squad during pre-season."
The Brumbies will kick-off their 2020 Super Rugby season against the Reds at GIO Stadium next Friday at the earlier time of 7:15pm.