O'Neill has returned to his native Australia to join Central Coast Mariners on a season-long loan.
The Clarets' midfielder links up with the New South Wales-based club ahead of the start of the new A-League season in October.
O'Neill joined the Clarets from hometown club Brisbane Athletic in 2015 and signed an initial three-year professional deal at Turf Moor the following year.
The 20-year-old has since made six senior appearances for the club, including three from the bench in the Premier League in the early months of the 2016/17 season, before productive spells on loan in League One with Oldham Athletic and Fleetwood Town in 2017.
“I'm coming on loan and I want to earn experience. I want to be involved and help the team push forward," said O'Neill
“If that helps me when it comes to Burnley then great, but at the end of the day I am here to help the Mariners win games.
“A long-term goal of mine is also to break into the Socceroos squad. Moving over to England at a young age makes you grow up very quickly.
“You're in a man's world full of very good footballers and you either float or sink, so my time at Burnley so far has been fantastic."