The additional time will allow the bidders to refine their final offers, the source told Reuters on condition of anonymity, adding that the administrator, Deloitte, was still seeking a binding deal with the winner by June 30.
Deloitte declined to comment.
Virgin owed creditors nearly A$7 billion ($4.86 billion) when it entered voluntary administration in April, with its long-running financial struggles exacerbated by the coronavirus pandemic.
The next phase for the parties on the final shortlist will include further engagement with stakeholders and aircraft financiers as they seek pacts on future terms before binding bids are received, Deloitte has said.
($1=1.4413 Australian dollars)