The Olyroos conceded three early goals against Sydney FC but showed glimpses of what they are capable of in a 3-0 defeat to the A-League champions.

In their first game since January, Australia's under-23s appeared off the pace in the opening 20 minutes with Paulo Retre, Trent Buhagiar and Alex Baumjohann getting on the scoresheet for the Sky Blues.

Graham Arnold's entirely home-based squad showed glimpses of their potential as the game wore on and were only denied a goal by one of their own - with Sydney's Olyroos goalkeeper Tom Heward-Belle called into action on multiple occasions.

The game at Jubilee Stadium, watched by a small crowd, served as a final warm-up for Sydney before they fly out to Qatar on Saturday to complete their AFC Champions League campaign - with their next group match on November 19.

Ryan McGowan's participation in the ACL group stage is uncertain after Sydney confirmed the defender tested positive for COVID-19.

McGowan has been in the UK since the Sky Blues' A-League grand final win in August and was due to link up with the travelling party in the Middle East next week.

"He'll be tested again shortly and will hopefully make a recovery in time to meet up with the boys later in Qatar," Sydney FC coach Steve Corica said.

The Olyroos will face A-League newcomers Macarthur FC on Tuesday night as they continue their preparations for next year's rescheduled Tokyo Olympics.

Sydney took the lead on five minutes when Retre stroked home an assist from Milos Ninkovic.

The lead was doubled 10 minutes later when Buhagiar headed home a right-sided cross from Rhyan Grant to cap off a sparkling Sydney move.

An Olyroos error led to the Sky Blues' third with Buhagiar turning provider as Baumjohann slotted home in the 18th minute.

It was a solid test for Sydney with Corica looking ahead to their four ACL games in Doha, starting next week against Shanghai SIPG, and then the new A-League season in late December.

"We've got clearance to go to Qatar now," he said.

"We've got some important games coming up.

"We want to go into the new (A-League) season full of confidence."