Lam, who was in town to present a report on the Kumuls World Cup campaign to the Papua New Guinea Rugby Football League Board, was apparently hit by an angry fan.
Lam flew back to Sydney the following day but it is not clear whether he reported the assault. Attempts to contact him were unsuccessful.
Sports Minister Justin Tkatchenko said he had heard of the attack through social media but had not received a report on the incident.
Word of the attack has been “public knowledge” since Sunday.
Tkatchenko described the incident as disappointing saying fans had no right to attack a coach or anyone for any reason.
He said the incident reflected poorly on the people but also added that Lam should have been more careful.
The PNGRFL is yet to make a statement on the incident.