Australia's Refugee Action Coalition said the guard stopped the Iranian man from moving between different parts of the compound and assaulted him when he objected.
The coalition's spokesperson Ian Rintoul said it's not the first time staff from the centre had been flown home before they could be questioned by PNG police.
"Even in circumstances where other people, detainees, have made complaints about guards and have been able to identify guards, most often they've been allowed to depart the island without any follow up police investiagtion," said Mr Rintoul.
