A WA Police officer, who is accused of assaulting two teenagers including a police recruit outside a Midland pub, is set to fight the charges.

Shane Michael Ferguson, 34 - a detective with the South East Metropolitan District - was allegedly involved in an altercation outside the 7th Avenue Bar and Restaurant while off duty in July last year.

Josh Prime, a 19-year-old police recruit who was also off-duty at the time, received a fractured eye socket during the incident and was taken to Swan Districts Hospital for treatment.

It is alleged Mr Ferguson also struck Mr Prime's friend Hayley Lloyd-Riley, resulting in soreness to the 19-year-old's face and neck.

Mr Ferguson has been charged with grievous bodily harm and assault.

Today, in Perth Magistrates Court, a lawyer for Mr Ferguson indicated he was preparing to go on trial in the District Court for the grievous bodily harm charge.

He will appear in court again next month.

An internal police investigation into the incident is also being conducted.