Melbourne City has confirmed Olyroo Aiden O'Neill is set for three months on the sidelines due a back injury.
The midfielder missed City's 2-1 win over Western United on January 16 after complaining of a sore back in training.
An MRI scan has revealed the injury is worse than City first thought and will keep O'Neill sidelined until late May.
The news is a blow to 22-year-old who had only just joined City on a three-year deal after spending time at English Premier League club Burnley.
O'Neill joined Burnley in 2016 but only made three appearances for the Clarets, spending most of his time on loan including stints at Central Coast and Brisbane Roar.
O'Neill's setback will also hamper his cause in pushing for selection in Graham Arnold's 18-man squad for this year's Olympics having been part of the squad which qualified for the Games in last year's Asian Under-23 championships.