The outgoing acting deputy chief constable of the PSNI has taken legal advice after he was not shortlisted for the permanent role.
Stephen Martin said the process needed to be rigorously fair.
The Policing Board is responsible for appointments and said they were made based on merit and openness.
Mr Martin told the BBC: “These processes need to be rigorously fair, they need to be lawful.
“If that were not the case I would certainly be shocked and grossly disappointed and would feel considerably let down.
“I have taken legal advice and the board are aware of that now.”
He added: “When you apply for a position, you weigh these things up carefully, you put a lot of personal investment into it, preparation, and when it doesn’t work out I think naturally anyone in my position would be disappointed.”
Mr Martin was appointed acting deputy chief constable in August 2018. He has 32 years of police service.
The senior officer was interviewed for the chief constable role but lost out to Simon Byrne.
A Policing Board statement said: “The recruitment process for the deputy chief constable position is based on the principles of merit, fairness and openness.
“It incorporates independent scrutiny at all stages to provide additional probity and transparency.
“As the process is ongoing the board will not be making any further comment.”
Earlier this week Ulster Unionist board member Alan Chambers withdrew from the process to appoint the new deputy chief constable.
In a statement he said: “I am writing to formally state my concerns at some aspects of the recruitment process which was run last week for the post of deputy chief constable of the Police Service of Northern Ireland.
“This is obviously a key post within the PSNI - second only to the post of chief constable itself - and whoever gets it will have a major role in delivering policing throughout Northern Ireland.
“It is therefore absolutely vital that whoever is ultimately appointed to that post is done so via a process that is rigorously fair.
“I regret to say that my experiences last week did not leave me with this impression.
“This is - to say the least - a most unsatisfactory state of affairs and I would therefore like it to be formally noted that my confidence in this recruitment process is less than it was at the start of last week, and far short of where it needs to be.
“Therefore, I wish to withdraw from this process forthwith.”
The board is holding a special meeting to make the appointment on Thursday evening.
