The two doctors based in Tobermory in the north of the island are a couple and have given notice they intend to withdraw from offering 24-hour emergency cover.
An island councillor has now called for a meeting with the Health Secretary, Alex Neil.
It is the latest blow to islanders who have already expressed serious concerns about the island's medical provision.
It was reported last month that the two GPs who cover the Ross of Mull would leave at the end of September, while there would also be one of the two in Salen going, out of the island's total of six general practitioners.
The islands of Ulva and Gometra also depend on the Mull doctors.
The islanders have said they were worried that while there are two ambulances on the island and two crews, only one crew is on at any given time.
This meant it could take it two hours to get from one end of the island to the other.
Councillor Mary-Jean Devon, who lives in Tobermory, said she would be seeking a meeting with Mr Neil.
She said: "The people on Mull and Iona are feeling very vulnerable and deeply concerned as to what might happen in an emergency, given there is only one ambulance to cover an island of 270 square miles."
NHS Highland, however, has made clear that when a GP practice opts out of providing 24-hour cover, the health board has a statutory obligation to make alternative provision.