Rugby Australia high performance manager Ben Whitaker said the team was shocked at the incident and the fact that Stannard would no longer be leading them during the April competition.
"It would have been James' third Commonwealth Games. He's an extremely important member of our team both on the field and off the field," Mr Whitaker said.
In a statement, Rugby Australia said Stannard was struck by a man after speaking with him outside a fast-food shop in Coogee.
Police described the attack as "unprovoked" and said Stannard did not know his alleged attacker.
