The senior doctors' union says the latest high-level resignation at the Canterbury District Health Board is troubling.
Chief medical officer Sue Nightingale announced her resignation on Friday.
It is the fifth resignation from the board's 11-member executive team since last month.
Chief executive David Meates quit earlier this month.
The Association of Salaried Medical Specialists says it is concerned about the further loss of experience, especially during a pandemic.
Executive director Sarah Dalton said Nightingale's departure is of particular concern.
"The chief medical officer is an extremely important member of the executive team from our point of view. So that further loss of continuity, that loss of experience in leadership, particularly with the Covid outbreak as it is once more, is really troubling to us."
Dalton said a review of the situation might prevent similar resignations.
"I think that would be useful and I would also note that the board chair was appointed, as was the Crown monitor, and so they were central appointments.
"Some kind of a review as to how things have come to this point may shed some light, may stop it happening in the future."