Most recent waiting time figures showed the number of people waiting for treatment had fallen by the biggest figure on record, standing at just under 757,900.
The Welsh Conservative health manifesto says the party would set up the NHS Wales Reserves Service, to give the health service a bank of staff that can be called up during periods of crisis.
Millar told BBC Wales: “Staffing of the NHS is a disaster in Wales at the moment. There hasn’t been effective workforce planning by the Labour government or indeed by their partners, so we need to make sure we’ve got a proper workforce plan.
“There are doctors out there in Wales at the moment who have just qualified. There are nurses who have just qualified, who don’t have a job, they don’t have any employment. And that’s ridiculous when you consider the situation that the NHS is in.”
He said the reservist plan “is to bring people back into the workforce at times of peak need, so that they can help us to get to grips with these challenges, that’s our focus”.
It would include “people who might have retired, people who may have left health professions for other things, other people who might work in the private sector from time to time, but might want to make themselves available to the NHS in order to serve their country”.