Football Federation Australia have investigated an unspecified off-field incident involving under-23s captain Riley McGree, Lachlan Wales, Nathaniel Atkinson and midfielder Brandon Wilson.

The Olyroos had been playing in AFC U23 Championship qualifying tournament when the alleged incident occurred at the end of March.

FFA have asked the quartet to explain their actions during an end-of-tournament night out in Phnom Penh after Sport Australia received a complaint about their behaviour.

An extensive investigation was initiated shortly after the complaint was received and took months to complete due to its complexity.

The players will face possible fines and suspensions if they are found to have breached the FFA's code of conduct.

Arnold was made aware of the complaint made against the four players when he returned to Australia after the tournament.

"The alleged misbehaviour has been the subject of a thorough investigation," Arnold said.

"I have, and always will, make it very clear to my staff and players of my expectations of them in camp. They are the public face of football in this country and abroad, and with that comes added responsibility.

"We now need to ensure the individuals concerned are given the opportunity to a fair process as required under the FFA's disciplinary regulations."

McGree, Atkinson, Wales and Wilson were all named in the national under-23s squad to play New Zealand in a two-game series last month. The findings of the investigation were presented to the FFA board on October 3.

The players involved have been offered support and counselling services while the FFA works with the players union on the matter.

Professional Footballers have offered support to all four players.

It comes as the Socceroos prepare to host Nepal in a World Cup qualifier at Canberra Stadium on Thursday.

Arnold says the incident won't affect their preparations nor overshadow the build up to the game.

"Most football folk are focused on the performance of the Socceroos [on Thursday]," Arnold said.

"Now, I look forward to a wonderful game and the [players] are coming along well as a group.

"The boys have turned up to camp in great shape. We've created a lot of depth over the last twelve months. It's an important qualifier and my expectations are very high.

"It's a great opportunity to show the great people of Canberra and fans of what we can do."